I've always thought that while OJ was almost certainly "in on it", that he had an accomplice or accomplices, and he may not have actually committed the murders. The son is as likely as any, and more so than many.
Given what's known about his son, his admitted fantasies about knifing someone, his having a short time earlier attacked a former employer with a knife, his issues with rage, and then the physical evidence, including the knife found in his storage locker, a picture of him wearing the same knitted cap as what was found on the scene of the murders, and the lack of any physical evidence against OJ (not a scratch on his entire body while Goldberg's hands had been beaten to a pulp) ... it all adds up to the son having done it. It's unclear whether OJ was there at the time or showed up afterwards. He's certainly complicit in covering up the crime, but he almost certainly didn't do it.
Many people have been wrongly convicted because the lazy police "zero in" on a prime suspect, putting blinders on, so that they ignore and "don't notice" other viable suspects, but then they don't have big money to spend on high-profile defense attorneys either.