With no witnesses to the murders of Nicole Brown Simpson and Ron Goldman, DNA evidence in the O. J. Simpson murder trial was the key physical proof used by the prosecution to link O. J. Simpson to the crime. Over nine weeks of testimony, 108 exhibits of DNA evidence, including 61 drops of blood, were presented at trial. Testing was cross-referenced and validated at three separate labs using different tests with no discrepancies found. The prosecution offered the defense access to the evidence samples to conduct their own testing, but they declined.
The defense summarized their reasonable doubt theory as "compromised, contaminated, corrupted". They argued that, during the collection phase of evidence-gathering, the evidence was compromised by mishandling and 100% of the DNA of the real killer was lost; and then contaminated during the processing phase, with Simpson's preserved DNA being transferred to all but three exhibits. They alleged that the remaining three were corrupted as the police planted that blood evidence.
Due to its abundance and exhaustive validation, the prosecution considered the DNA evidence infallible. However, at this time the public was unfamiliar with the precision and significance of DNA matching, and the prosecution struggled to get the jury to appreciate this. The defense, on the other hand, had to change strategies after neither of their forensic DNA experts would support their theory. The new strategy, according to defense attorney Alan Dershowitz, intended to elicit a cherry-picking response from the jury whereby they would discard all of the "mountain" of DNA evidence against Simpson if they could show "a few of the hills" were corrupted by police fraud resulting in a jury nullification for the murders via an error of impunity. Although three exhibits were allegedly planted, by his closing arguments, lead defense attorney Johnnie Cochran had focused on a single exhibit: the bloody glove found by detective Mark Fuhrman at Simpson's Rockingham home.
After his acquittal, all of the DNA experts returned to testify in the wrongful death civil trial.
Background Judge Lance Ito Judge Lance Ito made several important decisions concerning the DNA section of the trial. First, he allowed the defense to argue that some of the evidence was planted despite producing no evidence that it was. Next, he ruled that the prosecution must reserve at least 10% of the DNA samples for the defense to test themselves. The prosecution actually preserved nearly all the samples for the defense but they ultimately declined to test the samples themselves. Next, Ito allowed Dr. John Gerdes to testify about contamination in prior LAPD cases. In the subsequent civil trial, all of the decisions were reversed by Judge Hiroshi Fujisaki, who banned all allegations of police conspiracy and only allowed Dr. Gerdes to testify to confirmed cases of contamination, in this case only, of which there were none.
Thano Peratis Prison nurse Thano Peratis testified he drew an undocumented amount of blood from Simpson. When the defense asked him to estimate how much he drew, he stated approximately 8 mL. Records from the testing labs show that only 6.5 mL of blood could be accounted for, and the defense claimed that 1.5 mL was missing. During the rebuttal phase, Peratis testified again and clarified he believes he only took 6.5 mL as the records show.
Philip Vannatter Detective Philip Vannatter testified that Simpson volunteered to give some blood for comparison to the evidence samples. Peratis drew an undocumented amount from Simpson on June 13 at approximately 3:30 pm, sealing it in an envelope, and gave it to Vannatter. The detective documented what happened and hand-delivered the sample to criminalist Dennis Fung, who was at Rockingham collecting evidence at approximately 5:30 pm. Fung had arrived at Rockingham at 7:10 am. At trial, Peratis' documentation confirmed that the blood draw took place at 3:30 pm; the jail's security camera show that Vannatter left the jail at approximately 4:00 pm and the laserdisc recorder on his police car confirmed that he did drive for over an hour to get to Rockingham. The log book at the crime scene showed that the detective arrived at 5:20 pm; Fung's written notes confirm that Vannatter transferred custody of Simpson's blood at 5:30 pm and the envelope was still sealed. The blood of both Ron Goldman and Nicole Brown, taken at autopsy by Deputy Medical Examiner Irwin Golden, was booked immediately into evidence by Detective Vannatter.
Detective Mark Fuhrman never had custody of any of the reference blood.
Detective Vannatter's decision to take the blood directly to Simpson's home rather than booking it into evidence was criticized after the trial for even making evidence-planting possible. He defended his decision by noting Fung testified that the envelope was still sealed when he received it. The defense would allege the police stole and planted one drop of Simpson's blood on the back gate at Nicole Brown's home, not his home.
Prosecution case and witnesses
The only physical evidence linking Simpson to the crime was DNA evidence. The volume of DNA evidence was unique and criminalists felt they could reconstruct the crime with enough accuracy to resemble an eyewitness account. With over 100 exhibits, the defense would have to discredit all of them to establish reasonable doubt. The prosecution also produced corroborating evidence—hair follicles, clothing fibers from the victims, and fibers from Simpson's Ford Bronco—found with the exhibits to corroborate their theory of how the crime was committed.
Mistakes made during the evidence collection were highlighted and repeated during cross-examination by DNA experts, but the prosecution began offering evidence refuting the claim that the mistakes rendered the results unreliable. With three different labs cross-referencing the evidence with no discrepancies found during testing—as well as the defense declining to challenge the results by testing the evidence themselves—the prosecution expected a conviction.
Geraldo Rivera asked several jurors what their reasonable doubt was concerning the blood drops found next to the bloody footprints near the victims that were photographed hours prior to Simpson's blood being drawn. Those samples were sent to Cellmarks for testing, not the LAPD, and were shown to be Simpson's blood with chances of error being 1-in-9.7 billion. In response, juror Carrie Bess said that she thinks the blood belonged to Simpson's children; juror Marsha Rubin-Jackson said that she thinks Simpson's blood was left there next to the bloody footprints prior to the murders happening; and jury foreman Amanda Cooley said that she had no explanation for that incriminating evidence and stated that it did not factor into her decision of reasonable doubt.
Dennis Fung Criminalist Dennis Fung testified from April 3–5, April 11–14, and April 17–18, 1995. He testified to how the blood evidence was collected from the crime scene, from the white Ford Bronco, and at Simpson's home. He stated he arrived at Rockingham at 7:10 am. He also testified that Detective Philip Vannatter gave him Simpson's reference vial of blood when he was at Rockingham.
The cross-examination of Fung by Barry Scheck lasted nine days. Scheck's aggressive questioning, along with Fung's unusual willingness to volunteer confusing information while answering, made the prosecution scramble to explain his answers. He said he did not see a blood drop on the back gate in a photo from June 13 despite collecting blood from that spot on July 3.
Later, the prosecution found a photo that showed the blood was there on June 13. Fung also said he could not see blood on the socks that he collected from Simpson's bedroom. The prosecution later demonstrated that blood is only visible under a microscope. Fung also admitted that blood evidence was collected in plastic bags, not paper bags as recommended, and stored in a police van without being refrigerated for up to seven hours. Scheck aggressively tried to shake Fung's timeline about when he received Simpson's donated blood, hoping to show that police actually delivered it the following day, June 14, instead of June 13, giving them a whole day with Simpson's blood they could allegedly use to frame him. The 10-minute window was documented; though Scheck tried to discredit Fung's documentation by the fact that a page of Fung's notes had been replaced with a copy, the original page was found and shown to be exactly the same.
Andrea Mazzola Criminalist Andrea Mazzola testified on April 20, 1995, and from April 25–27, 1995. Her testimony was also interrupted by jury problems. She testified to much the same as Dennis Fung—the collection, storage, and transportation of evidence at the crime.
During cross-examination, the defense tried to portray Mazzola as inexperienced. She defended herself stating she had just moved to LA recently and had worked at the Kern County Police district as a criminalist for eighteen months. She admitted to a few mistakes at the crime scene while collecting evidence including using one swatch to collect blood from three separate spots in the Ford Bronco and occasionally not changing gloves when picking up different pieces of evidence. She also verified the blood evidence was kept unrefrigerated for up to seven hours after collection.
Collin Yamauchi Criminalist Collin Yamauchi testified from May 24–31, 1995. He was the first scientist to handle and perform PCR analysis on several key evidence items, including the glove and the sock from Simpson's bedroom in his Rockingham home. He testified that the blood of Simpson, Brown, and Goldman was on the glove: Brown's blood was found on the sock in Simpson's bedroom and Goldman's blood was found in Simpson's Bronco. All but one drop of blood collected by Fung and Mazzola was PCR testable.
During cross-examination he testified that during preparation for PCR testing that a reference card is created using Simpson's donated blood for comparison to the evidence items. When asked, he initially stated he was not sure he changed his gloves when he moved from the reference card to the evidence items but then remembered he did change his gloves. In either case, he maintains that he never touched any of the evidence items with his gloved hands and used sterile instruments to handle the items that were then changed between each item. The defense claimed that Yamauchi lied when he said he changed his gloves and did handle items with his gloved hands and transferred Simpson's DNA to the evidence items from the reference vial. Yamauchi denied this, stating that before and after each evidence item is tested a blank sterile control swatch is run to determine if cross-contamination like that occurred and all of the controls were negative. Yamauchi also pointed out the defenses DNA expert Henry Lee did not change gloves either when he examined the evidence items.
Gregory Matheson Gregory Matheson, chief forensic chemist at the Los Angeles Police Crime Lab, testified from May 1–5, 1995. His serology results revealed that blood drops found alongside a trail of bloody shoe prints leading from the victims matched Simpson's blood with the error rate being 1-in-200. Matheson stated that none of Mazzola's admitted mistakes would have resulted in contamination of evidence. Matheson also testified about the only drop of blood that was too degraded for testing found under Nicole Simpson's fingernails. The defense said that blood belonged to the "real killer" but Matheson said that blood was probably hers because that hand was found in a pool of her own blood and wet blood degrades quickly. Later criminalist Renee Montgomery, using a different test, proved it was Nicole Brown's blood.