The Abominable Dr. Phibes (1971)

Doctors are being murdered in a bizarre manner: bats, bees, killer frog masks, etc., which represent the nine Biblical plagues. The crimes are orchestrated by a demented organ player with the help of his mute assistant. The detective is stumped until he finds that all of the doctors being killed assisted a Dr. Vesalius on an unsuccessful operation involving the wife of Dr. Phibes, but he couldn't be the culprit, could he? He was killed in a car crash upon learning of his wife's death...