DNA testing in the Hank Skinner case began again in 2012
after the state of Texas dropped its objections after a fight that lasted over
a decade. After the release of
some preliminary data, the prosecution declared that it confirmed Skinner’s
guilt, as reported by Jordan Smith in the Austin Chronicle. Mr. Skinner’s attorney issued a
response stating that not all testing was complete and that defense experts had
not had a chance to examine the results yet. Skinner had been found guilty of murdering his live-in
girlfriend Twila Busby and her two grown sons. He claims that he is innocent, and there is an alternate
suspect in this case, Robert Donnell, who was Twila’s uncle.
Mr. Skinner’s DNA was found on 10 of 40 items tested. Many of the items tested appear to have
been blood, and they come from various locations around the house. There are profiles that belong to an
unknown individual or individuals, including one unknown profile on a knife
that has DNA deposited by Mr. Skinner and by Elwin Caler, one of Ms. Busby’s
sons. There is also an unknown
profile from a bloodstain in the sons’ bedroom. The unknown profiles may not be complete, but that is one of
several issues that further testing might resolve.
My conclusions at this time are that the advisory paints an
incomplete (therefore misleading) picture of the case and is overinterpreting
both the previous DNA results and the present ones. For example, the prosecution’s advisory summarized the
testimony of a witness who claimed that Mr. Skinner threatened her, but the
witness later recanted, a fact that was ignored. The advisory failed to mention
anything about two bloody handprints and bloody bootprints that have been
discussed in one
report on this case. "The State tested the bloody handprints against
those of Hank Skinner. Hank was good for the three handprints near the back of
the house. The handprint on the trash bag, and presumably the handprint on the
front storm door, belonged to someone else." The existence of the jacket,
the handprints that apparently do not match, and the bloody bootprints that are
not his size are some of the objections to the prosecution's case.
With respect to DNA profiling the first problem is that the
most compelling piece of exculpatory evidence, what one person identified as
Donnell’s jacket, has been lost before it could be tested. The jacket is stained with blood and
sweat. If either Donnell’s DNA
were found on the jacket or if some of the blood were Twila’s), that would
establish reasonable doubt, at the very least. However, at present there is no reference profile of Robert
Donnell (see also below). The failure
to obtain his profile could be a consequence of the investigatory tunnel vision
that has plagued this case, as a previous entry here indicated. I suggest that the State of Texas
exhume his body or obtain his DNA in some other way.
A second problem centers around whether Twila was sexually
assaulted on the night of her death.
The vaginal DNA profiling was performed by standard autosomal DNA
methods, in which DNA deposited by a possible perpetrator can become
overwhelmed by the victim’s own DNA.
There is nothing in the public record of Y-STR testing being performed,
despite its routine use in sexual assaults. The unique advantage of Y-STR profiling is that it involves
only the Y chromosome, which women do not have; therefore, a male contribution
to a mixture can be selectively amplified by the polymerase chain
reaction. Either the laboratory
did not do Y-STR testing, or it did but the results were not included in the
advisory. In addition the
fingernail clippings either showed Ms. Busby’s DNA, or they did not show any
DNA. Moreover, fingernail scrapings
can also be tested with Y-STR forensics, which has marginally higher sensitivity than autosomal testing.
Mr. Skinner’s attorney indicated that the defense has requested
additional testing; therefore, it is possible that Y-STR results will be
forthcoming.
A third problem concerns the existence of DNA from at least
one unknown person. The evidence
with respect to the knife appears inculpatory at first glance, yet it is
undisputed that Mr. Skinner was bleeding that night. It is likely that his
contribution to the knife DNA profile arose from his blood, and one obvious
possibility is that he cut himself while committing the murders. The defense
should raise two alternate hypotheses. There is chance that his profile arose
from casual use of this knife around the house prior to the murder. In addition, Mr. Skinner was incoherent
according to one witness due to a combination of alcohol and codeine; therefore,
his DNA could have been deposited by his possibly handling the knife at some
point after the murder when he was allegedly stumbling around the house. It is also undisputed that he was in
close proximity to the victims that night; therefore, positing that he handled
the knife, although speculative, is not unreasonable.
The Skeptical
Juror wrote, "Fresh blood drops were found on the sidewalk, near the
front door of the house where the murders took place. Those drops were tested. The DNA from those drops belonged
not to Hank Skinner, but to an unidentified male." The most recent DNA
profiling also did not test the gauze, even though it may have been used to
wipe the knife, which is odd. I
wonder whether this profile was similar to or different from the ones turned up
in the most recent round of testing, and I also wonder who the DNA donor(s)
is(are). The former question might
be addressed by treating the DNA from the blood drops on the sidewalk as
something like a reference profile.
DNA mixtures are sometimes deconvoluted by a process known as sequential unmasking, in which a forensic worker is given information about the reference
profiles in a gradual manner, only after completing a relevant portion of the
analysis. Yet even the mere
existence of blood from another person calls for an explanation. Was the blood fresh? If so, who was bleeding besides Mr.
Skinner, Ms. Busby, Mr. Caler, and Mr. Randy Busby, Twila’s other son
(all of whose reference profiles are available)?
Finally, a fourth problem is that one of the samples may
have been contaminated with some DNA from a laboratory worker. This kind of event actually happens not
infrequently in DNA profiling, but it does mean that the defense needs
to scrutinize the negative controls and machine logs to look for other evidence
of contamination. Negative
controls will detect large scale contamination that affects multiple items of
evidence, but will often not detect sporadic contamination affecting a single
sample, as Professor William Thompson has pointed out: “However, the same processes that cause
detectable errors in some cases can cause undetectable errors in others. If DNA from a
suspect is accidentally transferred into a ‘blank’ control sample, it is
obvious that something is wrong; if the suspect’s DNA is accidentally
transferred into an evidentiary sample, the error is not obvious because there
is another explanation — i.e., that the suspect is the source of the
evidentiary DNA.”
One hopes and expects that future rounds of DNA testing will
address some of these shortcomings.
Both the victims’ families and Hank Skinner deserve nothing less than a
full accounting of what happened that terrible night. However, the prosecutor brings charges in the name of the
people; therefore, every citizen has some responsibility for what happens in a
courtroom, including the times when there is a miscarriage of justice.
