Have you read the account from JM and the other witnesses that corroborate his account?
You have the "evidence" of the testimony of a drunk guy who apparently entered an apartment then refused to leave vs... pretty much everyone else and apparently the physical evidence.
How does this sound? Guy entered the apartment under what exact circumstances we do not know. Maybe he was lost. Maybe he knew the girl or someone else. He was told to leave. He began to argue and refused to leave. Finally he was threatened and left but then threatened or attempted to come back in. JM then punched him. Probably from having his bell run and being drunk, he then fell down the stairs. When the police arrived, he told a drunken story that clumsily attempted to white wash his own guilt. Now both sides have been told. It appears that he was in fact primarily at fault for the incident.