Zodiac Killer geographic profile by Kim Rossmo, Ph.D.

Geographic Profile

Zodiac Serial Murders San Francisco Police Department

January 2007

For Law Enforcement Use

Report Prepared by: D. Kim Rossmo, PhD Geographic Profiler ICIAF Full Fellow Center for Geospatial Intelligence and Investigation Department of Criminal Justice Texas State University San Marcos, Texas, 78666 601 University Drive Office: (512) 245-2006 Fax: (512) 245-8063 E-mail: [email protected]

Case Information Case ame: Zodiac Offense Type: serial murders Offense Dates: December 20, 1968, to October 11, 1969 Location: San Francisco Bay Area, California Investigating Agency: San Francisco Police Department Contact: Inspector Dave Toschi and Inspector Bill Armstrong Geographic Profiler: D. Kim Rossmo, PhD Agency: Center for Geospatial Intelligence and Investigation, Department of Criminal Justice, Texas State University Geographic Profile Report Date: January 31, 2007

Introduction Geographic profiling is a criminal investigative methodology that determines the most probable area of an offender’s search base through an analysis of their crime locations. Geographic profiling assists in prioritizing suspects and case information management. Crime sites are entered into a computer system (Rigel), which produces colored-coded maps called geoprofiles. These show the most likely area of the offender’s search base. For the vast majority of criminals, their search base is their residence and the terms are sometimes used interchangeably. But in certain cases the search base for an offender’s crimes is some other anchor point, such as their work site or immediate past residence. Some offenders employ a social place (e.g., bar, restaurant, etc.) or similar location as the base for their criminal activities. Others may be transient, either living on the street or nomadic to such a degree that they lack any real search base. Investigators should always keep these possibilities in mind. It is important to remember that a geographic profile deals in probabilities, not in certainties. It should therefore only be thought of as a tool to be used as part of an overall investigative strategy to find an unknown offender.

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The Geography of Crime Criminals do not choose their targets randomly. There is a strong relationship between an offender’s search base and the location of their crime sites. Consequently, the geography of a crime series can provide useful investigative clues. For a crime to occur there must be an intersection in both time and place between offender and victim. Crime is therefore the product of the criminal, the victim/target, and the physical environment (“where and when”).

People, criminals included, have their regular routine

activities, such as commuting to work, shopping, and visiting friends and family.

These

locations, and the travel routes between them, make up a person’s activity space or comfort zone. Criminals typically commit crimes in those areas where their activity space overlaps suitable targets. Because criminal offenders possess at least a limited rationality, they consider the rewards, risks, and effort involved in their target selection. Consequently, the most important influence on where criminals offend is where they go during their non-criminal activities. Most (but not all) crimes occur less than two miles from an offender’s residence. On the other hand, predatory criminals are less likely to commit their crimes too close to home because of a desire for anonymity.

Assumptions The geographic profile is based on certain assumptions which, if violated, might affect the accuracy of its results. The following assumptions have been made for the present analysis: •

The linkage analysis for the crime series is accurate and reasonably complete (i.e., the same offender committed the linked crimes, and there are not a significant number of unlinked crimes that should be part of the series).

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The offender is a local hunter, not a poacher (i.e., the offender is not commuting into the area to commit the crimes).

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The offender’s search base has not changed during the time period of the crime series (i.e., the offender has not moved).

The Zodiac murders occurred 38 years ago. These are old cases and access to original police and laboratory reports was limited. Consequently, the profile that follows is only based on the

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provided material. Whenever possible, original police reports were used. Additional relevant information could influence the findings of this analysis.

Linkage Analysis Four attacks were used in this profile: (1) Faraday and Jensen at Lake Herman; (2) Ferrin and Mageau at Blue Rock Springs; (3) Shepard and Hartnell at Lake Berryessa; and (4) Stines in San Francisco. Neither the Bates murder in Riverside nor the Johns “abduction” on Highway 132 was included as there was insufficient evidence to conclude they had been committed by the Zodiac. Other murders and disappearances attributed to the Zodiac are speculation only.

Analysis This crime series involves 4 incidents, 7 victims, and 7 locations. Offense address and date details are presented below in the Crime Site Locations and Offense Chronology tables, respectively. The geographic profile for this case is based on 6 locations. (Certain crime sites may have been excluded from the geographic profile for methodological reasons; any such sites are listed in italics in the Crime Site Locations table.) Generally, the more locations in a crime series, the more accurate a geographic profile. For the 6 sites used in the present analysis, the 70% confidence level for the geoprofile is approximately 10%. As the total hunting area covers 1,358 square miles, this means that 70% of the time the offender’s search base will be found in the top 139 square miles (some of this area is water and other parts are not populated). The following figures are attached at the end of this report: •

crime locations

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geoprofile

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peak geoprofile area (top 10%)

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peak geoprofile area (top 10%) in Google Earth

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peak jeopardy surface (top 10%)

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peak geoprofile area (top 5%) 4

While the geoprofile results are shown on a modern (2006) map, not all the displayed neighborhoods were developed at the time of the Zodiac’s crimes. A map of the Vallejo area in 1969 is shown at the end of this report, following the geoprofile images.

Search Base Area The Rigel analysis indicates the most probable areas for the offender’s search base are: 1) southeastern Napa County, including American Canyon and north Vallejo; 2) eastern Solano County, including east and north Vallejo, Mare Island, and Benicia; and 3) northern Contra Costa County, just south of Carquinez Strait, including Crockett. These results are supported by other analytic perspectives outlined in the profile discussion below. In particular, the road network analysis suggests a further focus of the geoprofile to the areas near Sonoma Boulevard and SR-37, including Mare Island and the Vallejo neighborhoods north of SR-37 to American Canyon (e.g., Rancho Vallejo). Possible work locations for the Zodiac include Mare Island Naval Shipyard, Benicia Industrial Park, or Humble Oil.

Using a Geographic Profile A geographic profile provides an optimal search strategy, not an “X that marks the spot.” The red and orange areas of the geoprofile represent the most likely region of offender residence, and the gray areas the least likely (see the color Profile Legend in the GeoProfile figure). A jeopardy surface is the geoprofile’s probability surface viewed in three dimensions. When using a geoprofile, consideration should be given to neighborhood characteristics, such as land use, zoning, and socioeconomic level that might influence where the criminal lives. There is no guarantee an offender will be found in the peak profile area, but all else being equal, suspects located there should be prioritized.

Geographic profiling is strictly an

investigative decision support tool, and a geoprofile must be considered in the context of all available investigative information (e.g., forensics, witnesses, tips, etc.). Not all types of crime series can be geographically profiled, but in appropriate cases the procedure may be quite useful.

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Profile Discussion The geoprofile results are supported by three other analytic perspectives. First, serial killers often commit their first murder close to home. The Zodiac’s knowledge of the “lover’s lanes” in Vallejo shows familiarity and strong local area knowledge. In contrast, his target selection at Lake Berryessa and San Francisco did not show any evidence of local area knowledge. Also, the time lapse between the Blue Rock Springs shooting and the Zodiac’s telephone call was approximately 40 minutes, even though the distance between these two locations is only 3.5 miles (7 minutes normal driving time). What did he do for that other half hour? One possibility is that he returned home and disposed of his weapon. If so, that means he most likely lived within a five-mile radius of the crime site. The Zodiac also knew to telephone the Vallejo Police Department, even though the Blue Rock Spring Golf Course and park area was an unusual offshoot of municipal jurisdiction, totally surrounded by Solana County (see the 1969 Vallejo street map at the end of the report). The Zodiac’s comfort zone clearly includes the Vallejo area. The Zodiac appeared less familiar with the Napa area. He telephoned the Napa Police Department, but Lake Berryessa is within the jurisdiction of the Napa Sheriff’s Department – something most regular visitors to the Lake would have known. Also, when he called the police, he reported the murders were “two miles north of Park Headquarters,” when in actually fact the crime site was only 0.7 mile north of Lake Berryessa Park Headquarters. The San Francisco murder differs significantly from the Zodiac’s other crimes. Up to this point he was hunting in locations (remote “lover’s lanes”) that had a good probability of containing his desired victims. Target selection was a function of area, not of an individual. However, it is unlikely the Zodiac was successful in all his searches; serial killers typically engage in extensive hunting activities, and for every attack there are many unsuccessful search attempts. In San Francisco, however, the Zodiac controlled the situation through his selection of victim type. The need for such control could be indicative of the distance the Zodiac had to travel to the crime site. Criminals who travel longer distances to offend are less likely to use uncertain target selection techniques.1

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By way of analogy, a shopper may be willing to run to the corner store to see if a particular item is available, but will first telephone if he or she has to drive across town.

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It appears that the Zodiac choreographed the Stine murder. He picked a target type (taxi cab driver) who he can be guaranteed of both finding and accessing. He then went to a target-rich environment: Mason and Geary in San Francisco’s Theatre District, near Union Square, with perhaps the highest concentration of taxicabs in the City. He directed the taxi driver to a preselected location at Washington and Maple,2 near the Presidio. He then escaped, undoubtedly to his nearby parked vehicle. If the Zodiac parked his vehicle near Washington and Maple, he needed to find some way of getting from Presidio Heights to the Theater District. The most likely option would have been to walk a few blocks down to California Street (or further to Geary Street) and then take an eastbound bus to Mason Street. The encounter site in the Theater District was chosen because it was a target-rich environment. But why did Zodiac select Presidio Heights for the murder site? Two factors suggest themselves. First, pedestrian and vehicle traffic is relatively low in a wealthy, low density neighborhood during the late evening (9:55 pm), minimizing the risk of witnesses. Second, this location must have worked into the Zodiac’s escape plan. Witnesses saw him walk north towards the Presidio and he claims to have disappeared into the “the park a block & a half away” (see below). His comment about being approached by police about three minutes after he left the taxi cab is consistent with stopwatch measurements we took at the scene. A normal walk from Washington and Cherry to Jackson and Maple took about 2 minutes, 50 seconds. The most likely route followed by the Zodiac is outlined in green in Figure 1 (the red dot represents the murder site). The Zodiac’s claim to have hidden in the Presidio is unlikely. Police quickly responded to the shooting. They knew the killer’s direction of travel. The area would have provided excellent conditions for a canine track, and seven dog units were deployed in the area of the Julius Kahn Public Playground at the north end of Spruce Street. Despite all this, the dogs apparently found nothing. This suggests the Zodiac escaped quickly by vehicle.

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The murder actually occurred one block to the west, at Washington Street and Cherry Street. This change was likely the result of some unexpected situational occurrence – someone walking down the street, parking their car, leaving their house – that made the Zodiac concerned about potential witnesses.

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Figure 1. Presidio, San Francisco, California, 1969. Source: San Francisco street map, Gulf Oil.

There are three likely locations where the Zodiac could have parked his vehicle. First, it could have been left on the street.3 As the original destination was Washington Street and Maple Street, the Zodiac most likely parked between two and four blocks away, and not on Washington, Cherry, or Maple. Considering his direction of travel, the most probably area is between Jackson Street and Spruce Street and West Pacific Avenue and Locust Street. The darkly illuminated north ends of Spruce or Locust would have been good possibilities. The second likely location

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According to Armond Pelissetti, , a retired San Francisco police officer who worked patrol in the area and was the first responding unit to the Stine murder, there was more available street parking in Presidio Heights in 1969 than today.

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would have been on West Pacific Avenue, which has several parking spaces on its south side. This area can be accessed on foot by climbing down a short drop from the north end of Cherry, Maple, Spruce, Locust, and parallel streets. This escape plan would have put a barrier between the Zodiac and responding San Francisco police vehicles. Even more effective would have been to park at the south end of Portola Street or MacArthur Avenue in the Presidio. By walking across West Pacific Avenue from the north end of Spruce Street, and through the Julius Kahn Playground, the Zodiac could have quickly reached his parked vehicle – a distance from West Pacific Avenue of about 200 yards (see Figure 1). He could then have driven north through the Presidio (which despite being a U.S. military reservation in 1969 was not a secure site) and over the Golden Gate Bridge. This escape route would have quickly put him out of reach of responding San Francisco police units. It is not known at this time, however, how difficult it would have been in 1969 for the Zodiac to park on the Presidio grounds during the evening (i.e., was a visitor’s parking permit required, how frequent were patrols and parking enforcement on its 1,491 acres, did the Zodiac have a military pass on his vehicle?). Second, an analysis of the road network reveals a pattern that points towards Sonoma Boulevard and SR-37 (see Figures 2 and 3). If an individual lived in northeast Vallejo (close to Mare Island or the neighborhoods north of its access point) and also worked at Benicia Industrial Park (site of the former Benicia Arsenal, deactivated in 1963) or Humble Oil, they would commute along SR-37, Columbus Parkway, and Lake Herman Road. This route goes by both the Lake Herman and the Blue Rock Springs murder sites. If a person wanted to go into central Vallejo instead of driving home (say for shopping or business purposes), he would travel west on Tennessee Street from Lake Herman Road, passing only 400 yards to the north of the Springs Road and Tuolumne Street payphone used by the Zodiac after the second shooting. And both northeast Vallejo and Mare Island are directly south of the Napa payphone, connected by SR29/Sonoma Boulevard.

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Figure 2. Vallejo Area Commuting Routes.

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Figure 3. Vallejo Commuting Routes. A retired Napa County Sheriff’s Department deputy thought the Zodiac did not reside in Vallejo because he used a payphone in Napa; apparently the usual route between Lake Berryessa and Vallejo does not go through Napa. But even if this were true, it only applies to someone residing in central or east Vallejo. It is straight south and only 11 miles (14 minutes normal driving time) from the Napa payphone to the intersection of Sonoma Boulevard and Mini Drive 11

in northeast Vallejo. Also, anyone who left San Francisco heading north on the Golden Gate Bridge (from the Presidio) to return to Vallejo would use SR-37. Figures 2 and 3 should be compared with the Peak GeoProfile Area (Top 10%) map at the end of this report. Third, the Zodiac’s communication shows familiarity with the Vallejo area. He provided certain geographic clues in his correspondence to San Francisco area newspapers and his telephone calls to police departments. Relevant sections are presented below with the key phrases highlighted in yellow.

“If you will go 1 mile east on Columbus Parkway to the public park you will find the kids in a brown car” (telephone call to Vallejo Police Department, July 5, 1969). “I am the killer of the 2 teen-agers last Christmass at Lake Herman and the Girl last 4th of July” (Vallejo Times-Herald; July 31, 1969). “This is the murderer of the 2 teenagers last Christmass at Lake Herman & the girl on the 4th of July near the golf course in Vallejo” (San Francisco Chronicle; July 31, 1969). “4. Girl was lyeing on right side feet to west” (Vallejo Times-Herald; July 31, 1969). “4 the girl was on her right side feet to the west” (San Francisco Chronicle; July 31, 1969). “Here is part of a cipher the other 2 parts of this cipher are being mailed to the editors at the Vallejo times & SF Examiner” (San Francisco Chronicle; July 31, 1969). “Here is a cipher or that is part of one. The other 2 parts are being mailed to the Vallejo Times & S.F. Chronicle” (San Francisco Examiner; July 31, 1969). “In answer to your asking for more details about the good times I have had in Vallejo, I shall be very happy to supply even more material” (San Francisco Examiner; August 4, 1969). “I was at this phone booth haveing some fun with the Vallejo cop when he was walking by” (San Francisco Examiner; August 4, 1969). “In that epasode the police were wondering as to how I could shoot & hit my victims in the dark. They did not openly state this, but implied this by saying it was a well lit night & I could see the silouets on the horizon. Bullshit that area is srounded by high hills & trees” (San Francisco Examiner; August 4, 1969). “I want to report a murder – no, a double murder. They are two miles north of Park Headquarters” (telephone call to Napa Police Department, September 27, 1979). “I am the murderer of the taxi driver over by Washington St & Maple St last night, to prove this here is a blood stained piece of his shirt” (San Francisco Chronicle; October 13, 1969). “I am the same man who did in the people in the north bay area” (San Francisco Chronicle; October 13, 1969).

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“The S.F. Police could have caught me last night if they had searched the park properly in stead of holding road races with their motorcycles seeing who could make the most noise” (San Francisco Chronicle; October 13, 1969). “School children make nice targ-ets, I think I shall wipe out a school bus some morning” (San Francisco Chronicle; October 13, 1969). “To prove that I am the Zodiac, Ask the Vallejo cop about my electric gun sight which I used to start my collecting of slaves” (San Francisco Chronicle; November 9, 1969). “Hey blue pig I was in the park – you were using fire trucks to mask the sound of your cruzeing prowl cars. The dogs never came with in 2 blocks of me & they were to the west & there was only 2 groups of barking about 10 min apart then the motorcycles went by about 150 ft away going from south to north west. Ps. 2 cops pulled a goof abot 3 min after I left the cab. I was walking down the hill to the park when this cop car pulled up & one of the m called me over & asked if I saw any one acting supicisous or strange in the last 5 to 10 min & I said yes there was this man who was running by waveing a gun & the cops peeled rubber & went around the corner as I directed them & I dissap-eared into the park a block & a half away never to be seen again” (San Francisco Chronicle; November 9, 1969). “I have become very upset with the people of San Fran Bay Area” (San Francisco Chronicle; June 26, 1970). “I do have to give them credit for stumbling across my riverside activity, but they are only findings the easy ones, there are a hell of a lot more down there” (Los Angeles Times; March 13, 1971).

Zodiac’s communications show evidence of knowledge of the area around his first crime site.

He knows the name of the nearby lake (“Lake Herman”), directions (“west”), and

topography (“high hills & trees”). He talks about the “north bay area” and the “people of San Fran Bay Area” – not of San Francisco or the City. He also threatens children in school buses, a more common target in suburban and rural areas than in urban areas. By contrast, he says little about the Bates murder in Riverside and provides none of the geographic or crime scene details associated with his confirmed crimes.

Mount Diablo On June 26, 1970, the San Francisco Chronicle received a letter and a Phillips 66 road map of the San Francisco vicinity from the Zodiac. The letter contained a cipher and the statement: “The Map coupled with this code will tell you where the bomb is set.” On the map, the Zodiac had drawn his trademark circle and cross, centered over Mount Diablo, with the numbers 0, 3, 6,

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and 9 at the north, east, south, and west points of the cross, respectively. He had neatly printed “is to be set to Mag. N” next to the 0 (see Figure 4). On July 26, 1970, the Chronicle received another letter that included the postscript: “PS. The Mt. Diablo Code concerns Radians & ^# inches along the radians” The cipher was never broken.

Figure 4. Phillips 66 Mount Diablo Map.

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Mount Diablo was sacred to many California Native American tribes and was regarded as their place of creation. In 1851, Colonel Leander Ransom chose the mountain summit as the initial point for determining base and meridian lines still used in official land surveys. An aerial navigation beacon was erected at the peak in 1928 and a television transmitter tower in 1954. The two main coordinate systems developed for surface navigation are the Cartesian (or rectangular) coordinate system and the less well known polar system. The Cartesian system uses x and y values, referenced from an origin, to indicate a point in space (e.g., degrees of longitude and latitude). The polar system uses an angle and a distance, referenced from a pole, to locate a position. The pole on the Phillips 66 map is the peak of Mount Diablo. By knowing an angle (to be measured from magnetic north according to the Zodiac’s instructions) and a distance, a specific location can be determined. The angle, in radians, and the distance, in inches, are apparently contained in the cipher; if so, the limited options for both the number of radian (0 to 6.28) and inches (0 to 7.54) may provide decryption clues. A radian is an angular measurement equal to approximately 57.3 degrees5. There are 2π radians in a circle (360 degrees = approximately 6.28 radians). To find the location of his school bus bomb, Zodiac informs us to set our 0 direction to magnetic north and measure an unknown number of inches along an unknown angle. He does not specify if we are to measure the angle in a counterclockwise or clockwise direction. The former is the standard method, but Zodiac’s numbering is clockwise. Magnetic declination varies with both location and time. Currently, magnetic declination on Mount Diablo is about 15.7° east (see Figures 5 and 6). However, in 1970, the declination was approximately 16.8° east (see Figure 7). Most important, however, was what Zodiac believed it to be at the time he wrote the letter and how carefully he did his calculations. The answers to these questions are not known.

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The exact number may vary depending on the size of the original map; the estimate of 7.5 inches was calculated on the basis of the map’s folds and the envelope width. 5

A radian is defined as the angle subtended at the center of a circle by an arc of circumference that is equal in length to the radius of the circle.

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Figure 5. Magnetic Declination in the Continental United States. Source: nationalatlas.gov (http://nationalatlas.gov/articles/geology/a_geomag.html).

Figure 6. Magnetic Declination in the San Francisco Bay area. Source: nationalatlas.gov (http://nationalatlas.gov/articles/geology/a_geomag.html).

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Figure 7. Historic Magnetic Declination in San Francisco. Source: nationalatlas.gov (http://nationalatlas.gov/articles/geology/a_geomag.html).

Interestingly, the first two Zodiac attacks (Lake Herman and Blue Rock Springs) fall along a line approximately one radian clockwise from 1970 magnetic north and the fourth attack (Washington and Cherry, San Francisco) falls just south of a line two radians clockwise (there is some variation depending on which map is used; see Figure 8). The location of the third attack (Lake Berryessa) does not fit this integer pattern. As the Zodiac stated the directions were to his (non-existent) school bus bomb, not his past murders, this is most likely a coincidence. It is wise not to read too much into his riddles. What the Phillips 66 map does tell us, however, is that the Zodiac was familiar with Mount Diablo, and knew some of its history. It also suggests he had navigational experience and was familiar with certain geometric concepts.

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Figure 8. Mount Diablo and Radian Measures from Magnetic North.

Temporal Analysis The Zodiac was a weekend offender. Two of his crimes happened on Friday night, and the other two on Saturday evening. This normally suggests someone with weekday commitments, such as a Monday to Friday job. Even Zodiac’s correspondence discusses his weekend criminal hunting times.

“If you do not print this cipher by the afternoon of Fry. 1st of Aug 69, I will go on a kill ram-page Fry. Night. I will cruse around all weekend killing lone people in the night then move on to kill again, untill I end up with a dozen people over the weekend” (San Francisco Chronicle; July 31, 1969). “I want you to print this ciph-er on the front page by Fry afternoon Aug 1-69. If you do not print this cipher, I will go on a kill rampage Fry night. This will last the whole weekend, I will cruse around killing people who are alone at night untill Sun Night or until I kill a dozen people” (San Francisco Examiner; July 31, 1969).

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The Zodiac accelerated his offending. The interval between the first and second attacks was 196 days, between the second and third attacks, 85 days, and between the third and fourth attacks, 14 days.

The Zodiac The Zodiac likely had military experience. During the 1960s, U.S. troops were deployed in Vietnam and the country still had the draft. Clear footprints linked to the killer were found at Lake Berryessa and investigators determined they were left by a style of low-cut military boot called Wing Walkers, issued to Air Force and Navy personnel and sold as surplus at the Travis Air Force Base near Fairfield, California. Both bomb diagrams (San Francisco Chronicle; November 9, 1969; April 20, 1970) suggested knowledge of engineering, electrical, and bomb design (though this information can also be obtained from any number of books). The Zodiac escaped from the Stine murder through the Presidio, a U.S. military reservation. Finally, the opening sentence of many of his letters, “This is the Zodiac speaking” (e.g., Vallejo TimesHerald; July 31, 1969), is similar to the phrase “This is the Captain speaking,” used by ship captains and airplane pilots (though the line has also passed into common usage). The Zodiac probably possessed the following characteristics in 1969: •

white male

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32 years of age6 (between 28 and 36years); 70 years of age in mid 2007 (between 66 and 74 years);

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short brown hair;

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5’9” (between 5’8” and 6’);

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210 pounds (between 195 and 225 pounds);

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10½ shoe size;

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worked a Monday to Friday job;

This estimate was determined from an offender age calculation program used in serial crime investigations.

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•

had military experience;

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was familiar with semi-automatic pistols;

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possessed knowledge of cryptography, either professionally or self learned; and

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had access to a dark-colored (possibly brown) sedan with a track width of 57” – consistent with a compact-sized car – registered in California.

The Zodiac signed his correspondence with a symbol comprised of a circle superimposed on a cross. Various ideas have been proposed to explain the origin of this trademark, including the theory that it represents the astrological zodiac, the crosshairs in a riflescope, a compass rose, the unit circle, and even a Ford hood ornament. A Google Internet image search, however, did not disclose any similar images representing the astrological zodiac.

Furthermore, riflescope

crosshairs do not extend beyond the circle, compass roses typically have 8 or 16 points, and the Ford hood ornament is a cross within a horizontally distended hexagon. The only genuinely matching symbol appears to be the logo used on Zodiac watches. According to a company representative, the circle and cross represent a watch face and the Swiss cross, and is not derived from the astrological zodiac. This may suggest the Zodiac Killer either possessed a Zodiac watch or was at least familiar with their brand and logo. Current prices for Zodiac watches range from $150 to over $500; it is not known what their products sold for in the late 1960s.

Suspects A geographic profile can be used to prioritize suspects (a lower hit score percentage indicates a higher probability). Optimal results are achieved by combining the geoprofile with other factors relevant to suspect prioritization in the case (e.g., physical description, criminal record, behavioral profile, etc.). Generally speaking, the impact of any evidence on the guilt of a suspect is increased or decreased by calculating the likelihood ratio – the probability of the evidence given that the suspect is guilty, divided by the probability of the evidence given that the suspect is innocent: P(E|G) / P(E|I). It should be stressed that a profile match is several orders of magnitude less

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significant than a forensic match, and the primary purpose of the former is for suspect prioritization and information management, not to determine guilt or innocence. In a criminal investigation, suspects are evaluated by the evidence – evidence is not evaluated by its fit to a particular suspect. At times, this maxim appears to have been forgotten in the debates over the Zodiac case.

Investigative Strategies A geographic profile cannot solve a crime; only physical evidence, a witness, or a confession can do that. Its role is to assist investigators in more effectively and efficiently reaching one of these case resolutions. Various investigative strategies can be based on a geographic profile. While specific approaches are best determined by the police investigators familiar with the case, some examples of tactics successfully used in the past are listed below. Suspect Prioritization.

Suspects with known addresses can be prioritized for follow-up

investigative work. The problem in many serial crime investigations is one of too many suspects rather than one of too few. Profiling can help manage large numbers of suspects, leads, and tips. Directed Patrol and Surveillance. The peak area of the geoprofile can be used to help direct saturation patrol and surveillance efforts. This strategy is most effective if the offender is operating during specific time periods. Neighborhood Canvassing. Neighborhood canvassing, information sign posting, community cooperation, media campaigns, and area searches, can be focused with a geoprofile. Specific areas can be targeted for leaflet distribution or directed mailings of letters from the police department requesting suspect information from the public. Police Record Systems. A geographic profile can be used to search computerized police record systems with address information (e.g., computer-aided dispatch, records management, and automated jail booking systems, sex offender registries, etc.). Offender description, modus operandi, behavioral profile details, and similar information can help modify the search criteria. Other Data Sources. Databases are often geographically based, and parole and probation offices, mental health clinics, social services offices, schools, and other agencies located in the peak

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geoprofile area may provide useful information.

Several commercial companies offer law

enforcement agencies the ability to search multiple personal information databases. DMV Searches. If suspect vehicle information is available, a geographic profile can be used to search registered vehicle and driver’s license files from state or provincial department of motor vehicle (DMV) records. A multi-parameter search (i.e., vehicle type, make, color, and likely owner address) can help narrow down thousands of records to a manageable volume. The age of the Zodiac case limits the number of available investigative options and several strategies that could be employed in an active case are no longer viable. Specific tactics that might be considered today are presented below (these should be considered as suggestions only, and some of them may already have been tried by police investigators): •

thoroughly reexamine the Lake Herman murder as serial killers are more likely to commit mistakes during their first crime;

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conduct further DNA analysis of the Zodiac’s envelopes in order to generate a DNA profile with a sufficient number of alleles to be entered into CODIS;

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enter crime scene gun evidence – bullet and shell casing – into the ATF’s NIBIN (National Integrated Ballistic Information Network) Program for IBIS (Integrated Ballistic Identification System) digital image comparison;

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submit all crime scene fingerprint evidence for national comparison (assuming this has not been done recently);

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use an attributional expert7 to analyze the Zodiac’s communications;

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use a forensic knot specialist to examine the remaining knots in the Berryessa rope;

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reassess known suspects and offenders by their position on the geoprofile, physical description, and match to the behavioral (psychological profile);

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conduct a targeted media strategy based on the geographic and behavioral profiles to generate new tips and leads; and

7 “Attribution” is the scientific investigation of authorship; it typically incorporates the study of sources and influences on a piece of writing.

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determine those vehicles driven in 1969 that had a wheel track close to 57”. If 1969 records are still available from the California DMV, this information could be used as follows to generate new suspects: 1) prioritize the zip codes in the peak area of the geographic profile; 2) search the 1969 California DMV records for all vehicles8 that are: (a) sedans; (b) have a wheel track of 57”; and (c) are registered to an address in a prioritized zip code; 3) cross-reference the registered owners of these vehicles to their driver’s license files and select those who fit the Zodiac’s description (gender, race, age, hair color, height, and weight); 4) further prioritize these addresses by mapping them on the geoprofile; and 5) evaluate these individuals by other known/suspected offender characteristics (e.g., military history, navigation and/or cryptography training, etc.), and the personality and background described in the behavioral profile. As the population of Vallejo in 1969 was approximately 50,000 (estimated), this winnowing process could well produce a manageable number of viable suspects.

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The California DMV does not record vehicle color, though sometimes this information can be determined by checking police traffic citations.

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References While this profile is based on original police reports, a California Department of Justice review, FBI reports, and newspaper articles supplied by Phoenix Pictures, the below reference materials were also used. Brantingham, P. J., & Brantingham, P. L. (Eds.). (1981). Environmental criminology. Beverly Hills: Sage. Brantingham, P. J., & Brantingham, P. L. (1984). Patterns in crime. New York: Macmillan. Budworth, G. (1985). Knots & crime. London: Police Review. Foster, D. W. (2000). Author unknown: On the trail of Anonymous. New York: Henry Holt. Foster, D. W. (2001). Policing anonymity. Ideas in American Policing (No. 5). Police Foundation: Washington, DC. Geberth, V. J. (2006). Practical homicide investigation: Tactics, procedures, and forensic techniques (4th ed.). Boca Raton, FL: CRC Press. Graysmith, R. (1976). Zodiac. New York: Berkley. Graysmith, R. (2002). Zodiac unmasked: The identify of America’s most elusive serial killer revealed. New York: Berkley. Kelleher, M. D., & Van Nuys, D. (2002). “This is the Zodiac speaking”: Into the mind of a serial killer. Praeger Publishers: Westport, CT. Rossmo, D. K. (2000). Geographic profiling. Boca Raton, FL: CRC Press. Rossmo, D. K. (2006). Criminal investigative failures: Avoiding the pitfalls. FBI Law Enforcement Bulletin, 75(9), 1-8. Rossmo, D. K. (2006). Criminal investigative failures: Avoiding the pitfalls (Part two). FBI Law Enforcement Bulletin, 75(10), 12-19. Rossmo, D. K. (2006). Geographic profiling in cold case investigations. In R. Walton (Ed.), Cold case homicides: Practical investigative techniques (pp. 537-560). Boca Raton, FL: CRC Press. Rudin, N., & Inman, K. (2002). An introduction to forensic D:A analysis (2nd ed.). Boca Raton, FL: CRC Press. Walton, R. (Ed.). (2006). Cold case homicides: Practical investigative techniques. Boca Raton, FL: CRC Press. Time-Life Books. (1993). Unsolved crimes. Alexandria, VA: Author. Using D:A to solve cold cases. (2002). NIJ Special Report (NIJ Publication No. NCJ-194197). Washington, DC: U.S. Government Printing Office.

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Crime Site Locations o.

Site Type

Location

1

murder

Lake Herman Road, Benicia, Solano County, CA

2

murder

Columbus Parkway, Vallejo, CA

3

telephone call

Springs Road and Tuolumne Street, Vallejo, CA

4

murder

Lake Berryessa, east of Knoxville Road, Napa County, CA

5

telephone call

1231 Main Street, Napa, CA

6

encounter

Mason Street and Geary Street, San Francisco, CA

7

murder

Washington Street and Cherry Street, San Francisco, CA

25

Offense Chronology o.

Site Type

Date

Day of Week

Interval

Time

1

murder

December 20, 1968

Friday

2

murder

July 4, 1979

Friday

196 days

11:55 pm

3

telephone call

July 5, 1979

Saturday

45 min.

12:40 am

4

murder

September 27, 1979

Saturday

85 days

6:15 pm

5

telephone call

September 27, 1979

Saturday

70 min.

7:25 pm

6

encounter

October 11, 1969

Saturday

14 days

9:45 pm

7

murder

October 11. 1969

Saturday

10 min.

9:55 pm

26

11:15 pm

Crime Locations

27

GeoProfile

28

Peak GeoProfile Area (Top 10%)

29

Peak GeoProfile Area (Top 10%) in Google Earth

30

Peak Jeopardy Surface (Top 10%)

31

Peak GeoProfile Area (Top 5%)

32

Vallejo, California, 1969 (Source: California State Automobile Association road map)

33