Bearing in mind ten .22 casings were observed at the crime scene, investigators must have considered more than ten shots were fired, to accommodate the perceived .38 bullet hole. Investigators eventually realized that that no .38 bullet was involved in the shootings, stating "Only one gun was used in the double slaying Friday night on Lake Herman Road, of Vallejo teenagers David L Faraday and Betty Lou Jensen, and in shooting up their car, it was learned positively Monday by Sheriff's Sgt Leslie B Lunblad. The investigator said that what appeared to be a .38 caliber bullet hole in the roof of the Faraday station wagon actually was made by a small caliber bullet as the same size as those that killed the two youngsters". The premise of one gun and one shooter, however, is inherently flawed - not only from the standpoint that just nine casings were sent and analyzed by the Department of Justice, Bureau of Criminal Identification and Investigation, but the interpretation of the evidence submitted. Nowhere in the DOJ report does it positively confirm that one gun was used in the Lake Herman Road murders. In fact, the following will show that there is no evidence proving that one shooter was responsible, and the switching to a 'lone crazed gunman' in the eyes of the investigators has no evidence to support such a claim.
The 'Physical Evidence Examination Report' was submitted on January 3rd 1969, and listed the following items for testing.
He can secure David Faraday in two ways - facing him with the gun pressed behind his left ear (meaning he is a right-handed shooter), or securing him from behind with the gun pressed to his left ear (meaning he is a left-handed shooter). Either way, David Faraday is now helpless to influence events. From a ballistics standpoint, there is every reason to believe David Faraday had his back to the Rambler at this point.
If the Lake Herman Road murders were achieved by one person, unknown to the victims, who simply wanted to murder the young courting couple - one has to ask - why extricate both David Faraday and Betty Lou Jensen from the vehicle at all? There was extremely limited visibility that night, and the couple were effectively boxed in their vehicle like sitting ducks. Furthermore, David Faraday was executed at point blank range, behind his left ear, evident by the stippling marks noted at autopsy. If you have both victims out of the vehicle, positioned side-by-side, with your supposed pencil flashlight targeting them, why not just shoot David Faraday from a couple of yards away, thereby eliminating any risk of engagement. The Zodiac Killer applied caution in his three other attacks, blindsiding Paul Stine at Presidio Heights, shooting Michael Mageau and Darlene Ferrin while they were penned inside their Corvair, and keeping his distance at Lake Berryessa until Cecelia Shepard had bound Bryan Hartnell. He never gave the male victims a chance to take any counter measures. Without meaning to sound insensitive - which is not the intention - the Zodiac Killer could have just shot David Faraday in the head, face on. There was never any need to get into a position where you are pressing the gun behind David Faraday's left ear. Engagement, this close to a potential victim carries risk - something the Zodiac never portrayed in any of his other attacks. The suggestion being, that one assailant was securing David Faraday as Betty Lou Jensen was fleeing across the turnout, powerless to act.
The Zodiac stated in the 'Debut of Zodiac' letter "What I did was tape a small pencel flash light to the barrel of my gun. If you notice, in the center of the beam of light if you aim it at a wall or ceiling you will see a black or darck spot in the center of the circle of light about 3 to 6 inches across. When taped to a gun barrel, the bullet will strike in the center of the black dot in the light. All I had to do was spray them as if it was a water hose". The Zodiac Killer was clearly referring to the murder of Betty Lou Jensen when he referred to "spraying them as if it was a water hose", because David Faraday was executed from near touching distance. This may suggest, that the person who wrote the letter is the assailant who fired into the Rambler and murdered Betty Lou Jensen, and is simply recollecting the night from the first person perspective, not his accomplice's - who never sprayed anyone. The second assailant would then coldly execute David Faraday with a single shot. One assailant fired 9 shots, the other just one. This is borne out in the Department of Justice report which we will analyze now.
(A) Cartridge cases: Semi-circular firing pin impression at 12 o' clock position, small extractor markings at 3 o'clock position. Very faint ejector marking at 8 o' clock position (latter may not always be detectable).
(B) Weapon barrel or test bullets: Six right hand grooves, land and groove ratio 1:1+. Bullet groove width approximately 0.056 inch. Bullet land width approximately 0.060 inch".
The report clearly states, that it must "not be assumed the exhibits must have been fired in such a weapon", but likely.
These exhibits, however, are missing two vital pieces of evidence - one bullet and one casing - of which could have been fired from an altogether different weapon. If you don't test all the items recorded at the crime scene, it is impossible to rule out two guns or two shooters.
It states that it "was possible to determine" that 6 bullets had right-hand twist characteristics, which could mean that the one recovered from David Faraday was either unable to be determined, or didn't have right-hand class characteristics like the other bullets (it may have had left-hand class characteristics, indicating a separate and distinct firearm). However, the key phrasing is "although some were damaged, it was possible to determine". In other words, it was possible to determine that the bullet recovered from David Faraday didn't exhibit the same characteristics as the other 6 bullets, otherwise the statement should have read "it wasn't possible to determine the characteristics from the bullet recovered from David Faraday". If the bullet was too damaged, it would have been impossible to determine if it exhibited 6 right-hand groove class characteristics like the others - but the fact it wasn't damaged enough - meant it had sufficient detail and was seemingly able to be compared.
We can rephrase the passage from "All bullets submitted were Western copper coated .22 long rifle bullets, although some were damaged, it was possible to determine ALL but Item  had 6 right-hand groove class characteristics", to "All bullets submitted were Western copper coated .22 long rifle bullets, although some were damaged, it was possible to determine Item  didn't have 6 right hand groove class characteristics". If the bullet recovered from David Faraday was too damaged, this distinction could not have been made.
A reminder to earlier: "Intercomparison of the cartridge cases in items 4 and 5 indicates that all are probably fired in the same weapon and all are the same make and type of ammunition. Due to lack of sufficient unique structure it appears that considerable difficulty will be encountered in identifying the responsible weapon if it should be recovered". Items 4 and 5 are the cartridge cases retrieved from the turnout floor, not the casing recovered from the Rambler floorboard. This tenth was likely the casing ejected when David Faraday was shot close to the open passenger door. This casing has disappeared and was never tested, leaving open the distinct possibility that the bullet recovered from David Faraday, which didn't exhibit the same characteristics as the other bullets tested, is inextricably linked to the missing casing. This means we could have a second firearm, and thus a second shooter.
The DOJ report added "The best bullets were those in items 2, 3 and 8. Each of these were microscopically compared with the others but in no case was an absolutely positive identification possible. This is apparently due to the condition of the rifle barrel, which does not leave coarse structure on bullets fired therein, as well as the effect of the copper coating on the bullet. From our examination it appears that a conclusive identification of the responsible weapon will be extremely difficult, if not impossible, should it be recovered". If you cannot identify the responsible weapon, you cannot be certain there weren't two, even if they were both J.C. Higgins Model 80 or otherwise.
With David Faraday standing by the right side of the Rambler, facing away, a weapon pressed up to the left side of his head from this position would likely eject the casing to the shooter's rear (toward the rear of the gun), in a direct line with the open door of the Rambler, either deflecting off the door or landing unimpeded onto the passenger side floorboard. If the bullet that killed David Faraday was distinct and separate to the other tested bullets, this 'missing' casing may hold all the answers.
If the markings on this casing are similarly unique, compared to the other nine casings, then it is not inconceivable that a link exists between the bullet and casing used to murder David Faraday - and may implicate a second assailant on December 20th 1968. There should have been a further item listed in the Department of Justice report:  'One Super X cartridge case found on the front passenger side of the Rambler station wagon". But there wasn't.
When we look at the Department of Justice report, coupled with the statements in the 'Debut of Zodiac' letter, it is not inconceivable that more than one person was responsible for the murder of David Faraday and Betty Lou Jensen back in 1968. The relentless pursuit of a single 'crazed maniac' may very well have been a false premise on behalf of the investigators, who likely dismissed this option far too early. The Lake Herman Road murders may have involved two perpetrators, with one falling by the wayside after the first crime, forever bound in silence. But there still remains a possibility that two could have been involved throughout the 'Zodiac' crimes. Whatever the case, the Department of Justice report has certainly left the door open to speculate.
Department of Justice report.