Fosco's source was Willie Messino. Willie was a long time made guy in the Elmwood Park Crew. Willie may have told Fosco a couple of harmless stories here and there, but Willie would have NEVER discussed murder details with a goof like Fosco.
Your right,Messino would never tell the whole thing to Fosco.Plus i sence some sort of personal hatred in his articles,aimed for example at DiFronzo.