Yes I know the killer or if 2 were involved they or at least 1 of them would likely know. But when potential suspects are investigated/interviewed non guilty 1s may not know that fact (clothes in the creek bed not whose clothes if any were there).
Or a tipster might mention it (maybe even the color of clothing?) and how and where did they get this specific info from about clothing or where other evidence may have been left and found by LE. I hope BG has a big mouth and has told someone even a minute bit of what happened etc
lease: JMO