After a local Post Office burglary, five suspects were being interviewed. Below is a summary of their statements. Police know that each of them told the truth in one of the statements and lied in the other. From this information can you tell who committed the crime?
Looking at Brian's statement if it was Charles, then Brian was lying in his first statement, which makes the second statement true. Which would mean that it was both Charles and Alan. So it can't be Charles.
Which means Derek was lying in his first statement, which makes the second statement true. Therefore it can't be Alan.
So Eric's second statement must be false, meaning his first statement was true, therefore it was Derek.