I certainly THINK, that most of Frank Sheeran’s claims sound fake... I don’t KNOW. I wasn’t alive for or near the action to know.
However, Frank’s seemingly fake claims can also bring about the truth. It can bring out someone to step forward and either claim ownership or, provide actual believable evidence that proves Frank’s claims wrong.

If Frank’s stock goes up because of these stories, jealousy and anger can brew up among some people.

Someone knows or knew who committed the unsolved crimes. Time will tell if they honor Omertà or recognize it has become, every man for himself.