With no witnesses to the murders of Nicole Brown Simpson and Ron Goldman, DNA evidence in the O. J. Simpson murder case 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.[1]
The defense summarized their reasonable doubt theory as "compromised, contaminated, corrupted".[2] 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.[3] 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.[4] The defense, on the other hand, had to change strategies after neither of their forensic DNA experts would support their theory.[5][6] 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.[7] 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.[8][9][10]
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