Doesn't this retard know how to lie? Tell as much of the truth as possible. Tell her you had a crush on her. If you tell her she was your girlfriend, she will check with the girls in your class.
The fuck? Why wouldn't you immediately go to the cops with the footage of the killing? The police aren't going to arrest you for going to the wrong bathroom. You can just say you had to take a mad shit and ran to the closest bathroom. They have footage of a double homicide, that's more important.