Four men (Andy, Ben, Cal, and Dan) eat dinner together at a square table in a restaurant. Suddenly, Andy cries out "I've been poisoned" and falls over dead. Andy's companions were questioned by the police and each made three statements, exactly one of which is false for each man, which are as follows:

__Ben__

1. I didn't do it.

2. I was sitting next to Dan.

3. We had our usual waiter today.

__Cal__

1. I was sitting across from Andy.

2. We had a new waiter today.

3. The waiter didn't do it.

__Dan__

1. Cal didn't do it.

2. The waiter poisoned Andy.

3. We had a new waiter today.

Assuming that only Andy's companions and the waiter are implicated, who is the murderer?

C3 and D2 contradict each other, so one of them must be a lie. That means that either C2 or D3 is true, but they both claim there was a new waiter today, so both are true.

Therefore, B3 is a lie, so B1 is true (**Ben is innocent**) and so is B2 (Ben sat next to Dan).

Therefore, C1 is a lie, so C3 is true (**the Waiter is innocent**).

Therefore, D2 is a lie, so D1 is true (**Cal is innocent**).

With three of them innocent,** the only possible murderer is Dan**.

Or, as Charlie pointed out, maybe there was no murder. Andy could have committed suicide, or the poisoning may have been an accident.