When you're sitting in a tiny concrete box and looking at the very distinct possibility of spending the rest of your life in such a box, either metaphorically or, in McAfee's case, literally, the thought process is quite different. Yes, McAfee has had run-ins with the law before, but maybe he figured he wasn't going to get out of this situation so easily, and he didn't have that many more good years left in front of him, concrete box or no.
Thus, I'm willing to accept this as a suicide unless and until compelling evidence otherwise surfaces.