Paul Connely was a doctor and friend of Kenny.
As Dr. Paul Connelly is preparing his friend Kenny for dental surgery, Kenny admits that he is no longer attracted to his wife because she's "too old." He then says that he skipped out on a camping trip with Dr. Connelly and his family because he was afraid of what he'd do to Dr. Connelly's young daughter. As Dr. Connelly becomes more and more agitated, Kenny blithely continues to speak, finally admitting to engaging in sexual relations with Dr. Connelly's daughter while she was at his house for his own daughter's sleepover. In a fit of rage, Dr. Connelly kills Kenny with his dentist's drill.
After he is arrested for Kenny's murder, Dr. Connelly commits suicide by hanging himself in his prison cell. Sam and Dean eventually learn that Veritas, the goddess of truth, was summoned in Calumet City, and anyone who wishes out loud for the truth will be bombarded with it until they die. Dr. Connelly was likely suffering Veritas' curse, which was why Kenny was compelled to tell him the truth. Veritas is a pagan deity and thus eats human flesh, and we see Dr. Connelly's partially eaten body in Veritas' home.