Yeah, some cons serving life or very long sentences will confess to murders just to help other cons out. That isn’t too uncommon.
However, if he has genuine “inside knowledge” of the murders that isn’t public, it probably merits investigation.
You would be surprised at how well inmates can communicate information within a prison or even from 1 prison to another.
I do remember enough about the story to know that Sanford was already well known to police at 14 years old.
Smothers says he confessed at the time and I have trouble believing the prosecutor wouldn’t have taken the easy conviction of Smothers if there was any doubt about Sanford’s guilt.