Slasher movies are a type of film where a costumed killer murders a group of friends in close succession. Whodunnit slashers are where the killer is one of the friend group, instead of being a supernatural force or human escapee.

Some movies play this like a fairplay mystery: by the finale, the clues lead to the murderer and no-one else. Most movies don’t: I can accept innocent characters being absent during (and only during) the killings with paper-thin reasoning as being necessary to ratchet up the drama, but characters picking up hobbies of “standing around in the dark” and “saying creepy phrases” (let alone jump scaring people) really aggravates me.

Older movies (e.g. the original Scream, April Fools’ Day (‘86)) seem to do this better, or perhaps are just easier due to expecting less of audiences – i.e., a lack of familiarity with particular tropes. Nowadays, the possibility of multiple killers is well-known, and audiences know to expect that a character who wasn’t attacked on-screen or lacks a shot of their corpse probably isn’t dead. Black Christmas (‘74) had a mix: the foreshadowing leads to one character, but it’s not him (and in the finale he gains the unfortunate habit of acting creepy and refusing to speak clearly), and the actual killer is never introduced on-screen.

In many modern movies, it feels like the finale would work just as well with somebody else as the killer. Scream II released decoy scripts where different characters were killers, and while these varied in thematic fit, they fit well enough with the clues on-screen. Oftentimes you can go back and read a particular scene a different way, but you can also do that for people who turned out to not be the killers: an ironic echo working whether or not someone turned out to be the murderer means you can’t use this aspect of the narrative to figure out the killer, though it is fun to try.