Didn't seem to me that the FBI were really all that competent along with Tony getting extremely fortunate breaks. Ray Curto especially since it would appear he had been a wired up informant from before the timeline of the show began. Personally, I don't think Tony was killed, but that's not the point. IF he was killed, what does Carlo have to offer the FBI at that point? He doesn't have any dirt on NY or anyone important and I doubt the FEDS really care about Benny, Walden, Patsy or Paulie. There's not much Carlo could give them is there? Like you said it's hearsay and his word against theirs. And If Tony wasn't killed, what does he have on Tony besides the usual RICO predicates. He never ordered anyone killed by Carlo, he had nothing to do with Fat Dom. Carlo never witnessed him ordering anyone killed either. I'm sure Tony would've probably taken a plea deal and did some serious time, but not be locked away for life or anything. Unless there's something really obvious I'm missing that Carlo could link him to. But his flipping came pretty much out of nowhere when his kid got busted so he was mainly looking for a get out of jail free card for him.

Tony should have never yelled at Carlo in the car that one time. You could tell how hurt he was when he told him he should start sucking dick because Vito was so much more successful than he. Ha.