Did he roll over?

OK, so that sounds like a question with an obvious answer, but around here nothing has an obvious answer. Last night I put Casey down for bed. Of course, he sleeps on his tummy (a big no, no, I know) so I put him down but his arm was under him and he looked a little crooked and up on his side a little. BUT I'm not going to mess with a sleeping baby. I figured he could situate himself. Well about 15 minutes later he starts crying. I go in there to find him on his back. So did he actually roll over or did he have some help by the way I laid him down? That is the question of the day.