As I recall he was having sex with another man’s wife while the man was there. The police believed that the husband killed him (with a lamp, if I recall.) Apparently, Bob Crain was a serial pervert who had sex with lots of married women. For whatever reason the case was not pursued.
From what I found, Crane was killed by a Mexican illegal alien drifter who was forcibly sodomized by Crane.
The Mexican waited for Crane to fall asleep in a drunken stupor and then cracked his skull open with the camera tripod.
All decadence, and especially homosexual perversion will ultimately bring hell and pain to the practitioner.