Police conspiracy allegation
The defense initially only claimed that three exhibits were planted by the police but eventually argued that virtually all of the blood evidence against Simpson was planted in a police conspiracy. They accused prison nurse Thano Peratis, criminalists Dennis Fung, Andrea Mazzola, and Colin Yamauchi, and Detectives Philip Vannatter and Mark Fuhrman, of participating in a plot to frame Simpson. In closing arguments, Cochran called Fuhrman and Vannatter "twins of deception" and told the jury to remember Vannatter as "the man who carried the blood" and Fuhrman as "the man who found the glove."
EDTA
The only physical evidence offered by the defense that the police tried to frame Simpson was the allegation that two of the 108 DNA evidence samples tested in the case contained the preservative Ethylenediaminetetraacetic acid, or EDTA. Ironically, it was the prosecution who asked to have the samples tested for the preservative, not the defense. The defense alleged that the drop of blood on the back gate at the Bundy crime scene, which matched Simpson, and the blood found on a pair of socks in Simpson's bedroom, which matched Nicole Brown, were planted by the police. In order to support the claim, the defense pointed to the presence of EDTA, a preservative found in the purple-topped collection tubes used for police reference vials, in the samples. On July 24, 1995, Dr. Fredric Rieders, a forensic toxicologist who had analyzed results provided by FBI special agent Roger Martz, testified that the level of EDTA in the evidence samples was higher than that which is normally found in blood: this appeared to support the claim they came from the reference vials.
FBI special agent Roger Martz was called the defense on July 25, 1995 to testify that EDTA was present in the evidence samples, yet instead said he did not identify EDTA in the blood, contradicting the testimony given by Dr. Rieders the day before. Initially, he conceded the blood samples "responded like EDTA responded" and "was consistent with the presence of EDTA" but clarified his response after hearing during the lunch break that "everyone is saying that I found EDTA, but I am not saying that". When the defense accused their own witness of changing his demeanor to favor the prosecution, he replied "I cannot be entirely truthful by only giving 'yes' and 'no' answers". Martz stated that it was impossible to ascertain with certainty the presence of EDTA, as while the presumptive test for EDTA was positive, the identification test for EDTA was inconclusive. Martz also tested his own unpreserved blood and got the same results for EDTA levels as the evidence samples, which he said conclusively disproved the claim the evidence blood came from the reference vials. He contended that the defense had jumped to conclusions from the presumptive test results, while his tests had in fact shown that "those bloodstains did not come from preserved blood".
Blood planting
The defense alleged that 1.5 mLs of Simpson's blood was missing from his reference vial. Prison nurse Thano Peratis stated during a preliminary hearing that he had withdrawn approximately 8 mLs of blood from Simpson. However, lab records showed only 6.5 mLs was accounted for. Gregory Matheson at the Los Angeles Police Crime Lab responded that Peratis never documented how much was actually drawn from Simpson so it is not a fact that any blood is actually missing. The prosecution then offered a video of Peratis stating he had made a mistake and believed he only drew approximately 6.5 mLs, as the records showed. The defense challenged the admissibility of this video because it was not under oath but Judge Ito allowed it because Peratis was hospitalized at the time and unable to appear in court. In closing arguments, the defense accused Thano Peratis of being part of a "cover-up" to protect Vannatter.
Back gate
The defense alleged that Simpson's blood on the back gate at the Bundy crime scene was planted by the police. The blood on the back gate was collected on July 3, 1995, rather than June 13, the day after the murders. The volume of DNA on that blood was significantly higher than the other blood evidence collected on June 13. The volume of DNA was so high that the defense conceded that it could not be explained by contamination in the lab, yet noted that it was unusual for that blood to have more DNA on it than the other samples collected at the crime scene, especially since it had been left exposed to the elements for several weeks and after the crime scene had supposedly been washed over. On March 20, 1995 Detective Vannatter testified that he instructed Fung to collect the blood on the gate on June 13 and Fung admitted he had not done so. The defense suggested the reason why Fung did not collect the blood is because it was not there that day; Scheck showed a blown-up photograph taken of the back gate on June 13 and he admitted he could not see it in the photograph.
The prosecution responded by showing that a different photograph that showed the blood was present on the back gate on June 13 and before the blood had been taken from Simpson's arm. Officer Robert Riske was the first officer to the crime scene and the one who pointed out the blood on the back gate to Fuhrman, who documented it in his notes that night. Multiple other officers also testified under oath that the blood was present on the back gate the night of the murders. The prosecution also pointed out that the media cameras present proved that Vannatter had never to the Bundy crime scene (Nicole Brown's home), where Simpson's blood was allegedly planted.
Bronco
Barry Scheck alleged that the police had twice planted the victims' blood inside Simpson's Bronco. An initial collection was made on June 13; the defense accused Vannatter of planting the victims' blood in the Bronco when he returned to Simpson's home later that evening. The prosecution responded that the Bronco had already been impounded by the time Vannatter returned and was not even at Rockingham.
Socks
The defense alleged that the police planted Nicole Brown's blood on the socks found in Simpson's bedroom. The socks were collected on June 13 and had blood from both Simpson and Brown but her blood on the socks was not identified until August 4. The socks were found by Detective Fuhrman, but the defense suggested Vannatter planted the blood. He had received both blood reference vials from the victims earlier that day from the coroner and booked them immediately into evidence. Vannatter then drove back to Rockingham later that evening to hand deliver the reference vial for Simpson to Fung, which the defense alleged gave him opportunity to plant the blood. Fung testified he could not see blood on the socks he collected from Simpson's bedroom but the prosecution later demonstrated that those blood stains are only visible underneath a microscope.
Detective Vannatter denied planting Nicole Brown's blood on the socks. The video from Willie Ford indicated that the socks had already been collected and stored in the evidence van before Vannatter arrived and footage from the media cameras present appeared to prove that he never went inside the evidence van when he arrived at Rockingham.
Glove
The last exhibit allegedly planted was the bloody glove found at Simpson's property by Detective Mark Fuhrman. Unlike the sock and the back gate, the defense provided no physical or eyewitness evidence to support their claim that the prosecution could then refute. Jeffrey Toobin published an article in The New Yorker months before the trial began, which cited a source in Simpson's defense team that they intended to accuse Mark Fuhrman of planting the glove with the motive being racism. Robert Shapiro later admitted he was Toobin's source.
Defense attorney F. Lee Bailey suggested that Fuhrman found the glove at the crime scene, picked it up with a stick and placed it in a plastic bag, and then concealed it in his sock when he drove to Simpson's home with Detectives Lange and Vannatter and his partner Detective Philips. Bailey suggested that Fuhrman had then planted the glove in order to frame Simpson, with the motive either being racism or a desire to become the hero in a high-profile case. Bailey also suggested that Fuhrman broke into Simpson's Bronco and used the glove like a paint brush to plant blood onto and inside the Bronco.
During redirect, the prosecution made numerous points to support the contention that Fuhrman did not plant the glove. They noted that by the time Fuhrman had arrived, the crime scene at Brown's home had already been combed over by several officers for almost two hours, and none had noticed a second glove at the scene, including Lt. Frank Spangler. Spangler testified that only one glove was found at the crime scene, by him and the other two officers who were there first, and that he had been with Fuhrman for the duration of Fuhrman's time at the scene. Spangler stated that he would have seen Fuhrman purloin the glove if he had in fact done so. Detective Tom Lange testified on March 8, 1995 that 14 other officers were there when Fuhrman arrived as well and all said there was only one glove at the crime scene. Clark added that Fuhrman did not know whether Simpson had an alibi, if there were any witnesses to the murders, whose blood was on the glove, that the Bronco belonged to Simpson, or whether Kaelin had already searched the area where the glove was found. Prosecutor George Clarke, who specialized in DNA evidence, wrote that it was difficult to refute the defense's corruption claim about the glove deductively because the DNA results would be the same whether it had been planted or not, so they used inductive arguments instead.
During cross-examination by Bailey, Fuhrman denied that he had used the word "nigger" to describe African Americans in the ten years prior to his testimony. A few months later, the defense discovered audiotapes of Fuhrman repeatedly using the word – 41 times, in total. The tapes had been made between 1985 and 1994 by a young North Carolina screenwriter named Laura Hart McKinny, who had interviewed Fuhrman at length for a screenplay she was writing on women police officers. The Fuhrman tapes became one of the cornerstones of the defense's case that Fuhrman's testimony lacked credibility. Clark called the tapes "the biggest red herring there ever was."
After McKinny was forced to hand over the tapes to the defense, Fuhrman says he asked the prosecution for a redirect to explain the context of those tapes but the prosecution and his fellow police officers abandoned him after Ito played the audiotapes in open court for the public to hear. The public reaction to the tapes was explosive and compared to the video of the Rodney King beating from a year prior. Fuhrman says he instantly became a pariah. After the trial, Fuhrman said that he was not a racist and apologized for his previous language, saying he was play-acting when he made the tapes, as he had been asked to be as dramatic as possible and was promised a $10,000 fee if the screenplay was produced. Many of his minority former coworkers expressed support for him. He pleaded no contest to one count of perjury after the trial, retired from the LAPD and relocated to Idaho.
On September 6, 1995, Fuhrman was called back to the witness stand by the defense, after the prosecution refused to redirect him, to answer more questions. The jury was absent but the exchange was televised. Fuhrman, with his lawyer standing by his side and facing the possibility of being charged with Perjury, was instructed by his attorney to invoke the Fifth Amendment to avoid self-incrimination to two consecutive questions he was asked. Defense attorney Uelmen asked Fuhrman if it was his intention to plead the Fifth to all questions, and Fuhrman's attorney instructed him to reply "yes". Uelman then briefly spoke with the other members of the defense and said he had just one more question: "Did you plant or manufacture any evidence in this case?" Following his attorney's instruction, Fuhrman replied, "I choose to assert my Fifth Amendment privilege."
Cochran responded to Fuhrman's pleading the Fifth by accusing the other officers of being involved in a "cover-up" to protect Fuhrman and asked Judge Ito to suppress all of the evidence that Fuhrman found. Ito denied the request, stating that pleading the fifth does not imply guilt and there was no evidence of fraud. Cochran then asked that the jury be allowed to hear Fuhrman taking the fifth and again Ito denied his request. Ito also criticized the defense's theory of how Fuhrman allegedly planted the glove stating "it would strain logic to believe that".
On June 15, 1995, Christopher Darden surprised Marcia Clark by asking Simpson to try on the gloves found at the crime scene and his home. The prosecution had earlier decided against asking Simpson to try them on because they had been soaked in blood from Simpson, Brown and Goldman, and frozen and unfrozen several times. Instead they presented a witness who testified that Nicole Brown had purchase a pair of those gloves in the same size in 1990 at Bloomingdale's for Simpson along with a receipt and a photo during the trial of Simpson earlier wearing the same type of gloves.
The leather gloves appeared too tight for Simpson to put on easily, especially over the latex gloves he wore underneath. Clark claimed that Simpson was acting when he appeared to be struggling to put on the gloves, yet Cochran replied "I don't think he could act the size of his hands." Darden then told Ito of his concerns that Simpson "has arthritis and we looked at the medication he takes and some of it is anti-inflammatory and we are told he has not taken the stuff for a day and it caused swelling in the joints and inflammation in his hands." Cochran informed Ito that Shawn Chapman contacted the Los Angeles County Jail doctor, who confirmed Simpson was taking his medication every day and that the jail's medical records verified this. Uelmen came up with, and Cochran repeated, a quip he used in his closing arguments: "If it doesn't fit, you must acquit".
The prosecution stated they believed the gloves shrank from having been soaked in the blood of the victims. Richard Rubin, former vice president of glove maker Aris Isotoner Inc. which makes the gloves in question, testified on September 12, 1995 that the gloves had indeed shrunk from their original size. He stated "the gloves in the original condition would easily go onto the hand of someone of Mr. Simpson's size." Darden then produced a new pair of the same type of gloves, which fitted Simpson when he tried them on.
After the trial, Cochran revealed that Bailey had goaded Darden into asking Simpson to try on the gloves and that Shapiro had told Simpson in advance how to give the appearance that they did not fit. On September 8, 2012, Darden accused Cochran of tampering with the glove before the trial. Dershowitz, a member of the Simpson defense team, refuted the claim, stating "the defense doesn't get access to evidence except under controlled circumstances."