PROVING THE CASE: THE SCIENCE OF DNA: DNA EVIDENCE IN THE O.J. SIMPSON TRIAL,
67 U.
William C. Thompson, Professor, Department of
Criminology, Law & Society, University of California, Irvine, California
The author was a member of O.J. Simpson's
defense team.
I. Introduction
To draw appropriate lessons from the O.J. Simpson case, one must have an
accurate appreciation of the strengths and weaknesses of the DNA evidence
against Simpson. Much of the public discourse about the case begins with the
premise that the DNA evidence proved Simpson's guilt conclusively and proceeds
quickly to an analysis of factors that might explain why the jury nevertheless
voted to acquit. This line of analysis generally leads to unflattering
conclusions about the fairness or intelligence of the Simpson jury and, more
broadly, to cynical conclusions about the capacity of the criminal justice
system, as currently constituted, to produce just results. The first section of
this essay challenges the underlying premise of this analysis. I argue that the
jury could quite reasonably have concluded that the DNA evidence against
Simpson deserved little or no weight.
The Prosecution Account
The prosecution argued that Simpson cut his hand while murdering the victims
and left a "trail of blood" from the Bundy crime scene, into his
Bronco, and back to his residence at Rockingham. According to the prosecution
account, the victims' blood was transferred to the Bronco because it was
splattered on Simpson and saturated the glove (which Simpson carried with him
until he dropped it behind his house). Nicole Brown Simpson's blood was pressed
on the sock at the crime scene; perhaps Nicole's bloody hand touched his ankle.
Simpson disposed of the other clothing that he wore to the crime scene but left
the socks in his bedroom because he did not realize they were stained with
Nicole's blood.
The Defense Account
The defense story had several elements.
Simpson Bled at His Home and in the Bronco. The defense argued that Simpson
accidentally cut himself at his home during the evening of the crime, perhaps
while retrieving a cellular phone from the Bronco, and thereby left drops of
his own blood inside the Bronco, on his driveway, and in the foyer of his home.
Simpson later traveled to
The Bundy Blood Drops and Rockingham Glove Were Contaminated with Simpson's DNA
at the LAPD Laboratory. LAPD criminalist Collin
Yamauchi admitted that he spilled some of Simpson's blood from a reference vial
while working in the evidence processing room and that shortly thereafter he
handled the Rockingham glove and the cotton swatches
containing the blood from the Bundy drops. The defense proposed that
some of Simpson's blood was inadvertently transferred to these evidentiary
samples, perhaps on Yamauchi's gloves or instruments.
DNA of the person who left the blood drops (possibly the true perpetrator)
could not be detected, the defense argued, because it was degraded and
destroyed due to mishandling of the Bundy samples. LAPD criminalists
collected the blood drops by swabbing them with wet cotton swatches. The
swatches were then put in plastic bags and left several hours in a hot truck.
The prosecution's experts all acknowledged that DNA degrades rapidly when blood
samples are left in a moist, warm environment, that degradation can render the
DNA originally in a sample untypeable, and that
subsequent contamination of such a sample by a second person's DNA can cause it
falsely to match the second person on a DNA test.
The defense argued that the pattern of the DNA test results fits neatly with
the cross-contamination theory. The quantity of DNA found on the evidentiary
items was small enough to be consistent with such an inadvertent transfer. On
the glove, the allele matching Simpson was found in samples from the wrist
notch, in an area where Yamauchi wrote his initials, and nowhere else. In the
blood swatches, the quantity of DNA consistent with Simpson declined in the
order in which Yamauchi handled them - that is, the first sample he handled had
the most DNA, and the later samples contained much less DNA.
To bolster further the cross-contamination theory, the defense presented
evidence of sloppiness in the LAPD's handling of
samples prior to DNA testing. The criminalists were
poorly trained with respect to sample handling, were not following a written
protocol, did not understand the purpose and importance of precautionary
measures, such as changing gloves, and made serious
errors even when attempting to demonstrate proper sample collection and
handling techniques. Defense expert Dr. John Gerdes,
who reviewed DNA test results at the LAPD laboratory during the year prior to
the Simpson case, found a history of serious contamination problems that he
attributed largely to cross-contamination of DNA due to poor sample handling
procedures.
Dr. Gerdes also found startling evidence of
cross-contamination in the DNA test results of the Simpson case itself: it
appeared that the reference vials containing the blood of Nicole Brown Simpson
and Ronald Goldman were contaminated with the DNA of O.J. Simpson! Extra alleles consistent with O.J. Simpson's appeared when the
victims' blood was typed both at the LAPD laboratory and at two other
laboratories to which the same vials were later sent.
The prosecution contended that cross-contamination of the Bundy drops was ruled
out because substrate controls (i.e., test samples taken from unstained areas
adjacent to the blood drops) were negative - that is, they contained no
detectable DNA. If the Bundy drops were contaminated with Simpson's DNA, then
the substrate controls should also have been contaminated. The defense had two
responses to this argument. First, it appeared from the laboratory notes that
the LAPD had failed to process and handle the substrate controls in parallel
with the Bundy drops, leaving open the possibility that the substrate controls
were not exposed when the cross-contamination occurred. Second, it is
well established that substrate controls do not always pick up DNA
contamination, even when they are handled in parallel with the contaminated
samples. Indeed, Dr. Gerdes testified that his review
of previous LAPD testing revealed numerous instances in which controls designed
to detect contamination were negative even though contamination had clearly
occurred. The prosecution neither challenged nor rebutted this testimony.
Switching of Swatches. After they were used to collect
blood at the crime scene, the Bundy swatches were sealed in plastic bags and
stored in a truck. At the end of the day, they were returned to the LAPD crime
laboratory and left in test tubes overnight to dry. The next morning, criminalist Andrea Mazzola
packaged the dried swatches in paper bindles. In a pretrial hearing about two
months thereafter, Mazzola testified that she had
placed her initials on each of the bindles.
When defense experts examined the bindles containing the Bundy swatches, they
made two startling discoveries: none of the bindles bore Mazzola's
initials, n14 but some bore what renowned criminalist
and defense expert Dr. Henry Lee later characterized as wet transfer stains -
the sort of stains that would be produced by contact with swatches that were
wet with blood. These observations led Dr. Lee to a memorable conclusion:
"something is wrong."
The Bundy swatches should not have been wet when they were placed in the
bindles, the defense argued. According to laboratory notes, the swatches had
been allowed to air-dry in open test tubes for fourteen hours before they were
placed in the bindles. Dr. Lee testified that the swatches should have been
completely dry within three hours. A study produced by the prosecution stated
that swatches dry within fifty-five minutes.
The defense suggested that one of the detectives took blood from Simpson's
reference tube, created swatches, and then stored the swatches in plastic bags until
an opportunity arose to substitute them for the Bundy swatches (perhaps
substituting the bindles as well). The tell-tale wet transfers occurred because
the detective failed to allow the swatches to dry adequately after removing
them from the plastic bags. The defense was able to establish, through
cross-examination of the prosecution's experts, that LAPD detectives are
trained in the collection of blood samples; detectives have swatches and
plastic bags for that purpose and often submit blood swatches to the
laboratory. Moreover, the lead detectives in the Simpson case had access to the
laboratory.
Lead detective Philip Vannatter also had access to
Simpson's blood. Blood was drawn from Simpson by Thano
Peratis, a nurse employed by the LAPD, the day after
the crime. Peratis placed the tube of Simpson's blood
in an unsealed envelope and gave it to detective Vannatter.
The defense established that LAPD policy calls for evidence of this sort
to be booked immediately, and that Vannatter could
have booked it within minutes at either of two locations. But he did not do so.
Instead, he kept Simpson's blood with him for at least several hours and, by
his account, drove across the city with it to Simpson's residence, where he
gave it to LAPD criminalist Dennis Fung. Whether Vannatter's account
is accepted or not, the defense argued, it is clear that he had sole possession
of Simpson's blood tube long enough to have removed blood and made some
swatches had he chosen to do so.
Furthermore, blood was missing from Simpson's reference tube. Nurse Thano Peratis testified at a
preliminary hearing that he had drawn eight milliliters (ml.) of blood from
Simpson. Under close questioning, he expressed confidence that the amount was
between 7.9 and 8.1 ml. n21 However, records in the LAPD Crime Laboratory
indicated that the tube had contained only 6.5 ml. when it was received by the
laboratory. The prosecution responded that Peratis
must have been mistaken about how much blood was drawn.
Nicole Brown Simpson's Blood Was Planted On the Sock. The blood matching Nicole
Brown Simpson that was found on the sock was a large, thick stain, slightly
larger than the size of a quarter. It had a slightly crusty appearance and made
the underlying material of the sock stiff and puckered. Surely this stain would
have been noticed, the defense argued, had it been on the sock at the time the
sock was collected. Yet on three separate occasions the sock was examined and
the stain was not noticed. On June 13, 1994, criminalist
Dennis Fung collected the socks in O.J. Simpson's
bedroom. At that time he was conducting a search for blood in Simpson's
residence. He noted no blood on the socks. On June 22, 1994, the socks were
examined at the LAPD laboratory by Michelle Kestler,
a laboratory supervisor, and two experts for the defense, Michael Baden and
Barbara Wolf. They noted no blood. On June 29, 1994, the socks were examined
again as part of an inventory of evidence ordered by Judge Ito. The express
purpose of the inventory was to determine what blood samples might be available
to be split with the defense. No blood was observed on the sock. The laboratory
notes say "blood search, none obvious." Then on August 4, 1994, the
blood stain was discovered. The defense argued that this sequence of events makes
it obvious that the blood was planted on the sock sometime after June 29, 1994.
Defense experts Dr. Henry Lee and Professor Herbert MacDonnell examined the
sock and concluded that the blood stain had been pressed onto it while it was
lying flat, and not while someone's leg was in the sock. The blood had soaked
through one side of the sock and left a "wet transfer" on the
opposite inner wall at a point that would have been directly under the stain
had the sock been lying flat. The wet transfer is inconsistent with the
prosecution theory, the defense argued, because Simpson's leg would have
blocked such a transfer had he been wearing the sock when the blood was
deposited on it during the murders. Based on Professor MacDonnell's estimates
of the drying rate of blood on the sock, the defense argued that by the time
Simpson got home and removed the socks, the blood would have dried, making a
wet transfer impossible at that point.
The planting theory is also supported by evidence that the chemical preservative
ethylenediaminetetraacetic acid ("EDTA")
was found in the stain, the defense argued. The victims' blood samples were
stored at the LAPD laboratory in tubes that contained EDTA. When the defense
first raised the theory that the blood on the sock had been planted, the
prosecution sent the sock to the FBI laboratory and asked that the stain be
tested for EDTA. Absence of EDTA would presumably have been taken as proof that
the stain did not come from the laboratory tubes. But the tests performed by
FBI agent-examiner Roger Martz did show evidence of the presence of EDTA. When
the prosecution declined to call Martz as a witness, he was called by the
defense. Martz admitted that the stain showed traces of EDTA but opined that
the quantity was too low to be consistent with blood from a reference tube. The
defense then presented Dr. Fredrick Reiders, who
reviewed Martz test results and expressed the opinion that the quantities of
EDTA present in the stain were indeed consistent with the stain originating in
blood from a reference tube, and are too high to be consistent with blood from
a living human being. The defense argued that Dr. Reiders
was a better qualified and more credible witness than Martz, who does not have
an advanced degree, and that Reider's conclusion, if
true, proves that the blood on the sock was planted.
O.J. Simpson's Blood Was Planted on the Back Gate. Most of the blood samples
from the crime scene were collected on June 13, 1994, the day after the
murders; but the three blood stains on the rear gate were not collected until
July 3, 1994. According to the prosecution account, these stains were simply
missed during the initial collection and were only noticed later. According to
the defense account, these stains were not collected the day after the crime
because they were not there at that time. The defense offered a powerful piece
of evidence to support the planting theory. A photograph taken the day
after the crime shows no blood in the area of the rear gate where the largest
and most prominent stain was later found. Barry Scheck introduced this photo
during his cross-examination of criminalist Dennis Fung. After displaying a photograph of the stains that Fung collected on July 3, Scheck then showed the photograph
of the rear gate taken on June 13. In one of the more memorable moments of the
trial, Scheck pointed to the area where the largest stain should have been and
demanded, "Where is it, Mr. Fung?" Mr. Fung had no answer, nor was Scheck's question ever answered
by the prosecution.
The defense argued that the planting theory was consistent with the quantity
and condition of the DNA in the samples from the rear gate. The other samples
collected at the crime scene, including those from the front gate, were highly
degraded and contained little typeable DNA. By
contrast, the samples from the back gate contained high concentrations of undegraded DNA. The defense argued that these samples
should have been somewhat degraded had they been exposed to the environment for
three weeks before being collected.
The planting theory was also supported by the FBI tests, which showed evidence
of EDTA in the samples from the back gate.
The Victims' Blood in the Bronco. The defense offered several explanations for
the presence of DNA consistent with the victims' in the Bronco. One
possibility, the defense argued, is that the victims' blood was planted in the
Bronco by detective Mark Fuhrman in order to frame Simpson. Under this theory,
Fuhrman swiped the Rockingham glove inside the Bronco in order to plant the
victims' blood there. Although the detectives testified that the Bronco was
locked when they first saw it and denied that anyone had opened the doors while
it was at Simpson's residence, the defense pointed to evidence suggesting that
Fuhrman had, in fact, opened the door of the Bronco. In his testimony, Fuhrman
reported seeing blood stains on the lower sill of the Bronco's door.
Photographs of the Bronco showed that there were indeed stains where
Fuhrman reported them, but they could be seen only when the door of the Bronco
was open.
Even if Fuhrman did not swipe the glove in the Bronco, he might have
transferred the victims' DNA there unintentionally, the defense argued. A photo
taken at the crime scene showed Fuhrman standing in a pool of the victims'
blood pointing at a glove. It was after this photo was taken that Fuhrman went
with the other detectives to Rockingham. If Fuhrman then entered the Bronco
looking for evidence, the defense argued, the blood consistent with Nicole
Simpson on the carpet could have come from Fuhrman's shoe. Fuhrman or another
officer who had a bit of the victims' blood on a sleeve or shirt cuff could
have accidentally swiped it onto the Bronco console while exploring for
evidence.
A third explanation is that the victims' blood was planted in the Bronco while
it was at a storage facility. On June 14, 1994, Dennis Fung
first collected blood from the Bronco. The defense established that it was a
general practice of criminalists, when swabbing
blood, to collect the entire sample. Three witnesses testified that they had
been in the Bronco after June 14 and saw no blood. On August 26, 1994, the
Bronco was again inspected and blood was found on the console in the same
location where Fung had collected the initial
samples. In the interim, the Bronco was left at an unsecured storage facility
where a large number of people had access to it and unauthorized persons were
known to have entered it looking for souvenirs.
Finally, the defense argued that there could have been tampering with the
Bronco swatches in the LAPD crime laboratory. If Nicole Brown Simpson's blood
was planted on the sock, then her blood and that of Ronald Goldman could have
been planted in the Bronco swatches as well.