For the Defense - Vol. 7, Issue 3 - 7

significance of trace DNA in a forensic case. Often
the prosecution will allege that the defendant's DNA
is the result of direct transfer, when there is, in fact,
no basis for this claim. This is a classic strategy of
misdirection by focusing on the Who?, when it is the
How? or the When? that should be asked.
CASE 1: PERSON
Evidence: The defendant's DNA was detected
somewhere on the complainant's body. No serological
analysis was performed, so it isn't known whether
the DNA is coming from skin cells, saliva, or some
other bodily fluid.
* CASE 1A: The person was intoxicated or impaired
with no accurate memory of the events.
Poor memory can be the result of recreational
drug or alcohol use, over/undermedication, mixing
medications, anesthesia, sleep deprivation, fatigue,
head trauma, mental handicap, or degenerative
neurological disorder, to name but a few. In any case
where the complainant is unable to provide clear
testimony of the events that transpired, it falls on
the evidence to speak for itself.
Studies on secondary transfer frequently show the
DNA of one or more unexpected individuals.2-5
many cases, they are unknown,2-4
In
despite having
DNA profiles of everyone in the lab. One possible
explanation is the disposable gloves themselves, as
they are not sold as DNA-free, nor handled that way6
(note that " sterile " does not mean free of DNA, but
free of infectious pathogens; a blood stain that has
been autoclaved is no longer infectious, but the DNA
remains viable). Paradoxically, the unknowns are not
as disturbing as the knowns. In one particular study,
the DNA of a volunteer's living partner was detected
in a controlled experiment, even though the partner
had never been to the lab.5
In order for this to
happen, the partner's DNA had to (a) be present
on the volunteer's hands, and then (b) sufficiently
persist through handwashing such that (c) there was
still enough to transfer onto an object in order to be
detected.
* CASE 1B: The person is deceased and unable to
give an account of the events.
If the person is deceased, the gap in information is
much greater than if the person were alive. Extreme
care must be taken, then, to interpret how such DNA
came to be on the decedent's body. In one case, the
boyfriend/defendant's DNA was detected on the
girlfriend/victim's body, without consideration of the
fact that they slept together on sheets that they had
intercourse on often and had not been washed in at
least two weeks. At trial, it was unknown whether
she had showered that day.
CASE 2: FINGERNAILS
Evidence: The defendant's DNA is detected under
the fingernails of a complainant or decedent. While
fingernails are a part of a person's body, they are
being treated as distinctly different here, due to the
implication of violence.
* CASE 2A: The victim and the defendant live
together.
There are numerous studies that show that
individuals who cohabitate will have detectable
levels of the other's DNA under their fingernails.7-9
Two studies found this to happen in 37% of the
participants, with 17% of which yielding sufficient
data for identification. Both studies also found
that individuals who habitually bit their nails were
less likely to have foreign DNA under their nails,
presumably because they either swallow it or simply
flood their own fingernails with their own DNA.
Several samples had either zero or a trace amount
of male DNA, most likely due to the overwhelming
proportion of female DNA. Those samples were
subjected to Y-STR analysis, a special type of DNA
analysis that ignores female DNA and allows the
male DNA to now be detected. Of these, 63%
yielded results of some kind, with some detecting
an unknown second male contributor (i.e., a third
individual).8
Such a profile is usually reported out
rather innocuously ( " additional minor/less intense
alleles were detected, but were too incomplete for
comparison " ), when, in fact, it might be that of the
culprit.
* CASE 2B: The victim and the defendant don't live
together but are acquaintances.
Even when two individuals do not cohabitate,
studies have shown that one can pick up detectable
levels of DNA from another.10,11
In fact, a study of
random individuals found that 13% of the population
had foreign DNA under their fingernails.11
* CASE 2C: The victim and the defendant are total
strangers.
The nexus between two apparently random
individuals can be incredibly small. Two examples are
especially harrowing, saved only by airtight alibis.
In 2011, a private lab based in the United Kingdom
linked an innocent man to a sexual assault when
Vol. 7, Issue 3 l For The Defense 7
For the Defense - Vol. 7, Issue 3

Table of Contents for the Digital Edition of For the Defense - Vol. 7, Issue 3
