

You can modify the finishing move-related variables using the console commands, set killmoverandom to and set decapitationchance to.

Source: UESP wiki, "Skyrim: Combat" talk page (edited to take into account the comments in reply to the original post) | TES wiki, "Kill Camera" article (edited to explain further)

killing an enemy while sneaking and remaining undetected will allow a Kill Camera, even if there are more enemies present. But this does not mean that only killing the last active/aggressive enemy will trigger a kill cam, e.g. Due to this, killing the last active/aggressive enemy will often trigger a finishing move / kill cam.

Kill Cameras will only be performed if killing the enemy will take the player out of the combat mode.Finishing moves are affected by the in-game variables, 'KillMoveRandom' (default: 50%), and 'DecapitationChance' (default: 40%) and various factors, some of which are: Source: UESP wiki, "Skyrim: Combat" articleįinishing / Kill moves are not completely random. Note that under the right circumstances, NPCs and Dragons will also be able to perform finishing moves, both against each other and against you. If the Savage Strike (One-handed) or Devastating Blow (Two-handed) perks are unlocked, there's a chance that this will be a decapitation. If you are within about 1-4 blows of killing an opponent, a "finishing move" animation may appear, depicting one or several fatal strikes from either a first-person view or third-person "KillCam".
