Kenneth Tigar makes his 6th and Final Appearance on Barney Miller. He played Stephan Koepeknie twice, once he thought he was a werewolf and this time he is possessed by Satan. He also played characters, Jesus Christ, Philip Pollock, Eliot Porter and Fletcher.
The case that Dietrich refers to is probably the case known as "The Devil Made Me Do It" case. The case concerns the murder of Arne Johnson's landlord, Bruno Sauls. Sauls was stabbed twenty two times, and Johnson was convicted of the murder. Johnson served five years of a 10 to 20 year sentence. The case was the basis of the book "The Devil in Connecticut", by Gerald Brittle. The 2019 movie The Conjuring: The Devil Made Me Do It (2021) was based on the case. With a slight correction, in that the judge disallowed an attempted defense of demonic possession based on it not being something that could be proved.
When Harris shows Father Clement the painting, Father Clement assumes that Harris' shrink has given him a Rorschach test, also called Rorschach inkblot test, a method of psychological testing in which a person is asked to describe what he or she sees in 10 inkblots, of which some are black or gray and others have patches of color. The test was introduced in 1921 by Swiss psychiatrist Hermann Rorschach.