There was a bus driver that worked for the count hospital. He was on his way to deliver twenty patients to the nearby mental hospital. Along the way, he got thirsty. He stopped at a bar for a few drinks.
When he returned, he found the bus was empty. Somehow, the mental patients had escaped and were now roaming free. He was worried he might lose his job. Then, he got a brilliant idea.
He got on the bus and drove down the road a bit. He stopped at a bus stop and picked up everyone there. Then, he proceeded down the road to the asylum. Once there, he told the doctors that the patients on the bus were especially violent and needed to be restrained.
It took the staff months before they realized the mistake. By that time, many of the same replacements had gone insane. None of the original patients were found.