Heather Davey's killer has gone to supposedly great lengths to set her murder up so that it will be thought of as part of the series of 'Daisy Chain' murders. The jacket has been rigged, he can be first on the scene. Why on earth, then, would he arrange for the 'murder' to take place inside a locked gymnasium? Why not set off the booby trap in the hallway? She's on her own. Nobody would have seen what actually happened, and it would have been a lot more likely that the murderer might have escaped unnoticed. Instead, he arranges it in a locked room, with an impossible escape for the supposed killer that just draws attention to the whole thing. Poetic licence maybe, but it makes no real sense. Two other things that are very dubious: this is a large gymnasium in a modern college. Fire regulations would surely have made it impossible to build this without at least one other exit (having another exit would again have given the killer a possible escape and made setting it in the gym feasible). The second is that is the killer himself who draws attention to the flecks of blood on the jacket she'd been wearing and tells them it wasn't hers! He's talking to a reporter and a magician's aide - he wouldn't have to repeat it, and he'd be far less likely to be caught!