Red Herrings.
A red herring is the name given to another device which is intentionally
 used to divert the audiences attention from the truth or an item of significance.
can work with other devices such as enigmas, to create suspense.


For example:
in ‘saw’ two characters spend time imprisoned in a room in which a third character lies dead.
 Throughout the film, both characters appear to be guilty of a series of murder, until it is discovered
 at the end that the third person in the room is not actually dead... but is in fact the killer.