This is repulsive. OJ Simpson wrote a book and is doing a series of interviews describing, "theoretically," how he would have murdered his ex-wife Nicole Brown Simpson and her friend Ronald Goldman if he had done it.
The obvious (and now irrelevant) ethical issue is OJ's culpability in the first place. The trial was probably flawed, but because of double jeopardy he can't be tried twice for the same offense even if he confessed publicly. Double jeopardy is limited to being tried twice by the same sovereign, or authority, but he's clear on that because the murder happened in California and he was tried in California.
His book and these interviews are exploiting the public's obsession with this trial. He's also exploiting a painful situation and renewing the agony of the victims' families, who have already lived through it once. And what about Fox's responsibility? Is Fox being unethical by profiting from a mistake that the justice system made?
I think so.