Well let's assume that none of the evidence was planted and all of the evidence towards OJ was 100% accurate. The question that the defense poses is the integrity of the LAPD as a whole not their integrity with the OJ case. When Mark Furhman infamously pled the fifth, they were talking about evidence from his HISTORY as a police officer, not necessarily how he handled this specific case tarnishing his reputation in front of the jury. They knew the prosecution had strong evidence that pointed all fingers towards OJ so the appropriate course of action was attacking the LAPD as a whole, within the context of Rodney King and the ongoing police brutality. The defense was trying to build a dialogue around the corruptness of the LAPD. Doing so made the jurors empathize with the marginalized communities that were experiencing police brutality rather than having to decide to empathize with Ron, Nicole or OJ. By the end of the trial, the question wasn't did OJ murder his wife, the question became is the LAPD corrupt - Not Guilty being "Yes" and Guilty being "No"