by KYW's Tony Hanson

Philadelphia police have arrested a 20-year-old man in connection with the murder of a teenage friend in Kensington on Sunday.

Investigators say the victim was apparently shot while he slept.

According to police, defendant Arnaldo Torres-Santiago (pictured above) and 16-year-old victim Omar Rodriguez had been arguing -- possibly over who was tougher. Then Rodriguez apparently fell asleep. And at that point, police allege, Santiango shot him in the back of the head.