Four suspects are being interviewed at the scene of a murder. Each of the suspects is asked a question. Their answers are as follows:

Jack Vicious: "Sid Shifty committed the murder."
Sid Shifty: "Jim Pouncer committed the murder."
Alf Muggins: "I didn't commit the murder."
Jim Pouncer: "Sid Shifty is lying."

Only ONE of the four answers is the truth. Who committed the murder?

Alf Muggins.

If it was Jack Vicious, the statements of Alf Muggins and Jim Pouncer would be true. If it was Sid Shifty, the statements of Jack Vicious, Alf Muggins and Jim Pouncer would be true. If it was Jim Pouncer, the statements of Sid Shifty and Alf Muggins would be true. Therefore it is Alf Muggins, and only the statement of Jim Pouncer is true.