Answer:
He is refusing to incriminate himself during trial.
Explanation: The purpose of "pleading the fifth" is to stop yourself from saying anything that could contradict your side of the story when you are testifying in court. Thus, if someone WERE to do this and get caught in a lie, this is called self-incrimination. Because the man refuses to answer any questions about the case, he is refusing to incriminate himself during trial.