It would not surprise me in the least if the jury was multi-racial and the overwhelming majority of jurors were African-Americans. However, I am not convinced that the racial composition of the jury is a direct explanation for Simpson's acquittal. I know that blacks were supposed to have supported him and celebrated his acquittal - and I am not in any great doubt that he did it, by the way - but I think the real reason they let him go wasn't his race, as such, it was because realistically the African-American jury members individually must have been known to the local 'black' community and they must have worried about their own and their families' safety if they found him guilty. Given that the prosecutors and that unfortunate police officer struggled with the case and the evidence, it was an easier option for the jurors to acquit him and use the non-probative racial aspects of the trial as a pretext to salve own consciences, rather than face their friends, colleagues and families after issuing a guilty verdict.
In hindsight, this is obvious when you also consider the context of the case and the background events, including the infamous Ford Bronco chase that transformed Simpson overnight from aloof 'coconut' figure, looked on by ordinary black Americans with a mixture of respect and dislike, to a ridiculous sort of outlaw folk hero. It is the irony of ironies that O. J. Simpson, of all black people, found himself in the thick of a race-baiting trial. He had successfully transcended his racial origins and had become an accepted American sports celebrity, not really seen as 'black' at all, and many ordinary blacks viewed him with disdain as a sort of social 'turncoat'. Yet when his chips were not just down but gone, blacks turned out for him and the black racial agitators saw their opportunity and co-opted him. Yes, that part of it was all about race, but I think it does the jury a disservice to imagine that they would have acquitted him for a brutal double murder just because he was black. The actual jury decision was in my view more likely to have been about the jurors' own safety. The trial should have taken place outside Los Angeles.
One thing I am slightly surprised about is that Simpson was not more amenable to Shapiro's efforts to secure a manslaughter plea. Shapiro was known as a fairly conciliatory criminal defence attorney who was good at striking deals. Given the probable facts (on the basis of assuming Simpson's involvement), manslaughter would have been plausible and I would not be surprised if some sort of plea deal was in fact offered to Simpson behind the scenes along those lines.
I saw an interview with Shapiro once. He talked about the case and implied the obvious when he remarked rather coldly that there is a distinction to be made between legal guilt and moral guilt. I slightly disagree with him there, though I can see what he is getting at. I think what he meant is that there is a distinction between legal guilt and culpability - a more correct word. Guilt concerns liability, moral agency, consequences and punishment; culpability touches on involvement, blame and responsibility. The two overlap but are different things.
The whole point of the adversarial trial system is that legal and moral guilt are deliberately conflated. The jury in its deliberations goes through essentially a three-stage process. The jurors first ask themselves what we might call 'the culpability question': On the evidence presented, did the accused commit the acts or omissions alleged? If they decide he did so, then they must ask themselves 'the guilt question': On the evidence presented, did the accused act under a guilty mind when he committed these acts or omissions? If they decide he did so, then they are entitled to convict, though they have the option not to do so, if - for whatever reason - they do not want to punish somebody who is otherwise guilty. That is the (often overlooked or forgotten) third stage of their deliberations, since a jury is sovereign and the arbiter of both law and fact. This, I believe, is roughly what happened in the Simpson case. The jurors, especially the black ones, realised that if they returned a guilty verdict they and their families could be burned out of their homes. The theatrical weaknesses in the prosecution evidence conveniently allowed them to rationalise their counter-factual verdict. "The evidence was not strong enough to convict him" is what one tearful black lady juror told a radio host soon after the trial. Actually, the evidence was strong enough. We know because the whole thing was televised, which means we saw most of what the jury saw (a good argument, incidentally, for televising criminal trials).
Fortunately, unlike in England & Wales, wrongful death is a tort in the American system; this allowed for the limited correction of a probable error of impunity a couple of years later when the Goldmans and Browns brought and won a wrongful death suit against Simpson.