After 15 yrs I don't think that anyone's conscience is bothering them too bad! We always hear about so called "death bed" confessions but I can't think of a one that has ever checked out, on this case or any other.
I think the FBI profiler who made the statement in the press that one or more didn't feel good about their involvement in the case was just trying to drive a wedge between co-conspirators in an effort to get someone to come in and make the first move. Obviously that didn't happen.
I would welcome MHP's involvement, especially after their recent success in the Jackie Johns case and the arrest of Gerald Carnahan. For all we know, they may be looking into the case now.
Otherwise, I'm reminded of the SPD detective who said early on that this case is "unsolvable".