David Berkowitz- Son of Sam

I don't know if any proper explanation of this nickname was ever given. From what I know, the name comes from a letter that was sent to the newspaper in which a an who cliaimed to be the killer referred to himself as the "Son of Sam" and that is how he was known from then on

There were two "Sam's".  One was Sam Carr, the father of the two Carr brothers who were members of the devil worshipping cult.  The other was the demon, worshipped at Halloween since ancient times, called Samhain.  The cult worshipped Samhain, among other demons.  It was Sam Carr's dog, Harvey, that did the incessant, tormenting barking.   David actually shot the dog once, to shut it up, but it recovered.