You are right. I'm sure OJ's mom still believes in her son.
This could be right, but they could also fully believe they could convict him of anything now. Look at this thread: there isn't many here who don't already think he did it. Nobody here investigated, they are all taking the word of the police department and other known information. The DA may feel they have not only a good but great chance to get a conviction just because of the moood of the public.
I hope for justice's sake three things: one, the scenario I described above is not the case and they believe they honestly have the evidence that leads them to believe he did it; two, if he did do it, he gets the gas chamber; and three, if he didn't do it, he gets acquitted and the DA and police face some sort of review to explain why they focused on the guy that didn't do it and ignored anyone else that did.