I wonder why Williams did not just tell the cops this the afternoon he was making his statement when he saw Oswald brought into custody. Would have saved us much anguish. Oswald, the guy who was gunned down in police protection less than two days later....that guy.
I agree, Williams did see the assassin. If it was Oswald as the Lone Assassin who had just been arrested, Williams would have no fear of telling the authorities, he would have the authorities on his side and would have been hailed a hero.
So that leaves us with two possibilities as far as I can see:
Williams was totally innocent, maybe saw the assassin and was told to leave.
or
Williams saw the assassin because he was an accomplice.
For me, the weight of evidence available leans heavily towards the latter possibility. Rowland spots the man with the rifle around 12:15pm but I think it has been adequately demonstrated that Williams didn't go down to the fifth floor until the last minute so he's up there for the best part of 15 minutes. If spotted he would have been shifted immediately. The only real problem with Rowland's description of the black male in the SN is his age. Willams' lunch is found on top of a stack of boxes that form the SN indicating he was either in or right next to the SN as he had lunch.
The big problem with Williams' lunch evidence is that it reveals the conspiracy. It reveals Oswald could not have been alone if he was the Lone Assassin.
The mystery I'd like to solve is why the evidence was taken by the FBI, returned, then taken again. Something v. fishy going on there.