PROVING THE CASE: THE SCIENCE OF DNA: DNA EVIDENCE IN THE O.J. SIMPSON TRIAL,
William C. Thompson, Professor, Department of Criminology, Law & Society, University of California, Irvine, California
The author was a member of O.J. Simpson's
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.