There were at least three spurious confessions to the Sacco-Vanzetti murders. Of course, at least one of those was probably elicited by a bribe from the defense team . . . so that's not exactly the same situation.
I think there's a good chance this guy is just a loon who is obsessed with the Ramsey murder and has somehow convinced himself that he did it.
The "undisclosed details" thing here won't wash. Too many people were blabbing all sorts of stuff during the initial investigation. I'm sure there were plenty of leaks that never gained any public notice.
One Question:
Why not arrest the guy, bring him here...doo the due dilligence and check out the whole story, including DNA..and then, announce this to the Press?