You need probably at least 6 players for this game, but this really is a case of the more the merrier.
Nominate one player to be the “detective”, and send him/her out of the room.
When the “detective” has gone, choose one of the remaining players to be the “murderer”. The murderer and all the remaining players then sit in a large circle facing each other.
The “detective” is called back in, and stands in the centre of the circle.
The “murderer” now has to “kill” off all the other players by winking at them. The “detective” has to try and work out which of the players is the murderer before all the other players are murdered. The other players are not allowed to give the game away to the “detective”, and usually “die” in a highly dramatic and noisy fashion!
A less blood-thirsty variation is to nominate a “leader” instead of a “murderer”, who performs certain actions that the rest of the group must follow. The “detective” has to work out who the leader is. Good actions are clapping, stamping feet, waving, slapping knees, etc (i.e. the whole group is clapping, and suddenly switch to stamping their feet).