Now that we have discussed negligence, how would you respond to the following situation?

Peter is a young graduate student who meets Joan at a folk dancing class. They go out on a few dates, but Joan decides to stop seeing Peter and tells him that she is not interested in entering into an intimate relationship with him. Nevertheless, Peter becomes obsessed with Joan and begins to stalk her.

After Joan's rebuff, Peter becomes extremely depressed and paranoid. He seeks psychiatric help from the campus psychiatrist, Dr. Martin, and he tells Dr. Martin that he wants to kill Joan. Dr. Martin tells the campus police and Peter is detained for awhile, but is later released by Dr. Martin's supervisor at the University. Peter later befriends Joan's brother and moves in with him. At no time is Joan or her family told of Peter's threats against her. Several months after his release, Peter carries out the plan that he had confided to Dr. Martin by stabbing Joan to death.

Joan's family sues Dr. Martin and the University for negligence.

What must they show in order to win their case?