1) the knife wasn’t one of a kind
2) the old man’s testimony probably concluded that things were taken out of context
3) the boy returned home, the old man couldn’t have possibly been able to make it to the stairwell in 15 seconds as he claimed
4) it was possible that because the boy was under emotional stress he was unable to remember the name of the film at the movie theatre
5) the old woman might have not been wearing her glasses.