The images on the right are of Cheri Jo Bates trousers being tested in the laboratory and the crime scene photograph taken in the Riverside campus alleyway on October 31st 1966.
The promotion attached to the upper image states "AISOCC Review Board Member Suzanna Ryan, Sal LaBarbera and Detective Kenneth Mains used the M-Vac System to extract DNA from clothing of a potential Zodiac victim at our AISOCC Laboratory. What they found after 50 years is shocking....tune into the History Channel on November 14th at 10.00 pm Eastern Standard Time to find out more...."
Suzanna Ryan specializes in forensic serology and DNA analysis, with over 15 years experience in the field. Forensic serology is the detection, classification and study of various bodily fluids such as blood, semen, fecal matter and perspiration, and their relationship to a crime scene.
The M-Vac system is used in such instances when a victim (in our case Cheri Jo Bates) has been grabbed or manhandled, and the perpetrator has left touch DNA, invisible to the naked eye. The M-Vac system is capable of extracting the touch DNA, to enable the laboratory to generate a genetic profile of the suspect. It uses a wet vacuum system in which a buffer will be sprayed onto the trousers, while at the same time the freed particles will be sucked into a collection bottle for testing. It is used when other techniques have failed, such as swabbing and taping. The samples collected may be incredibly small, so polymerase chain reaction (PCR) is often used to amplify the sample. The sample could be semen, skin cells, saliva or blood. "The M-Vac was able to collect anywhere from 36% to 189% more DNA from experimental evidence items such as extremely dilute blood (1:5000 – 1:25,000) on shirts, rocks, and wood and from touch DNA on knit caps and duct tape." Ryan Forensic.
Since 2002, when Cydne Holt secured a partial DNA profile of the Zodiac Killer from communications mailed by the killer, the field of forensic DNA analysis has come a long way, including the detection and examination of the male Y-chromosome in mixed samples. "The Y chromosome DNA testing enables examination of the male-specific portion of biological evidence. This capability can be especially important in situations where a small amount of male DNA may be recovered in the presence of excess female DNA, such as in sexual assault evidence." link.
The murderer of Cheri Jo Bates could easily have cut himself while inflicting the numerous injuries on the young woman, either from his hand slipping down the knife as it became soaked with blood, or quite possibly from the knife folding in on itself, had it broke or malfunctioned. The author of the 'Confession' letter did state "I plunged the knife into her and it broke. I then finished the job by cutting her throat." Clearly no knife blade was recovered at autopsy or on the alleyway floor, so if the author of the 'Confession' letter was truthful, it is most likely the killer had a small-bladed pocket knife which could easily have closed onto his fingers or hand, secreting blood onto the clothes of Cheri Jo Bates.
The promotion material promises "what they found after 50 years is shocking." So, if the hype is to be believed, we would have to assume that the M-Vac system possibly retrieved incriminating DNA evidence, likely from the trousers of Cheri Jo Bates, although one would expect her upper garments are the more likely area to have contained the fingerprint of the killer. However, touch DNA samples can produce erroneous and misleading results, the sample being so incredibly small, it is extremely susceptible to contamination. Hope you enjoy the series.