I always believed he killed himself, what I point out is the fact that they facilitated his suicide. They "check" late, they left him with sheets, etc. that they would not have had if he had remained on suicide watch. The most visible prisoner in the prison due to infamy, and they dropped the ball, and the timing seemed to suggest it was done with purpose.
He was hours away from suicide watch, he's moved to the Special Housing Unit from the cell they use for those on suicide watch (those cells usually have no anchor points, no exposed pipes, usually the bed is a mattress on the floor either with no sheets or with tear resistant sheets that are designed to make it difficult to fashion a noose), and the guards didn't follow the checks schedule. The Special Housing Unit has bunks to anchor to, regular bedsheets, sharp corners on some fixtures, etc. and is unlike the suicide watch cells.