Just jumping off your post. He might very well have something to gain by saying anything. Way back in the old days there was the Danielle Van Dam case. Despite the fact that divulging some of the details of their not quite conventional lives would be frowned upon by many, the parents of Danielle Van Dam laid everything out on the table. There were a few that thought her father had something to do with it, but he kept saying he had nothing to do with her disappearance (which he didn't). When you have laid your life bare, tell LE to check everything, give them anything and everything they want, people tend to believe you. When you hide, avoid the truth, try to pretend like anything you did that might not have been conventional either did not happen or was OK, people tend to think you have something to hide. JMO.
Seriously, if a person that was suspected by many came forward and said :"I had a relationship with X from this date to that date. It was not my proudest moment and it hurt people I cared about. There were communications between myself and person X on this date because "insert reason here". I had nothing to do with this person's disappearance. " that would sway some people. When you hide nothing, people think you have nothing to hide. JMO.