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.