DNA transfer in strangulation; differentiation vs hanging
Hi Catsmate,
Let me flesh out comment #25, but with the caveat that everything below regarding DNA applies to manual strangulation, not strangulation via a rope or something similar. In 2002 GN Rutty and Collaborators
wrote, "A total of 29 separate experiments were performed using a single male offender-female victim combination to observe whether DNA was transferred both from the offender's fingers to the victim's neck and vice versa and to consider the period of time after the event during which the material could potentially be recovered and amplified. DNA was amplified from either the victim's neck or the offender's fingers for at least 10 days after the contact although it is discussed whether this is potentially due to primary contact or a secondary/tertiary transfer event." I was surprised at the 10-day period.
GN Rutty and collaborators followed up in 2008: "The results of phase 3 showed that primary, secondary, and zero transfer of victim and/or offender DNA could be observed after physical contact and that alleles from an unknown source could still be detected in this more controlled experiment. The data presented in this paper demonstrate that DNA profiles generated after swabbing the skin surface of healthy adults can include components of an unknown source, present due to adventitious transfer. These components, if present in large quantities, have the potential to interfere with DNA profile interpretation of swabs taken for the investigation of physical assault by DNA profiling." There is also work from another group that studied swabbing technique in simulations.
Link.
I had thought that in the cases of male perpetrators strangling female victims, the biggest problem was the presence of the victim's DNA; therefore, I thought that Y-chromosomal DNA profiling would be the next logical step to try in experiments following on Rutty's work. The passages I quoted above point to different problem, namely third party DNA and innocent DNA transfer.
The other work that I had mentioned was work in which Peter Gill, one of the most accomplished investigators in DNA forensics, had participated. They wrote, "Partner's DNA was observed to accumulate during the day and to persist when an individual was absent from the shared home environment. DNA from unknown contributors was found on the neck of individuals that used public transport, attended public spaces and had social interactions. The data acquired from this study will help to increase knowledge on the composition of DNA present on an individual's neck in a daily situation." If Dr. Polkinghorne's DNA were found in a neck swab, he might have a plausible claim of innocent transfer.
In comment #22 I suggested than one might ask which methods can differentiate strangulation from hanging. What little reading I have done suggested to me that a person might void their urine either during strangulation or handing; therefore, I am not confident that identifying the stain in question as urine (comment #19) would have been probative.
"What many people consider to be hanging is not actually hanging, since death occurs by fracture/dislocation rather than asphyxia. [6, 7]"
link. I don't know much about the subject, but the interested reader could look into hyoid fracture.
Link. I have not found an indication that during the trial, the fracture or lack of fracture of the hyoid bone was discussed, but I did catch a
glimpse that the issue of damage to some cartilage was brought up. I am not taking any position on guilt or innocence.
