I was watching the first season, when Tony has Jimmy whacked for being a rat.
Big Pussy was currently under the mobs investigaton which had tony going nuts. Jimmy getting out of jail fast was odd, so Tony assumed his source mistaked Jimmy for Pussy, both of them being fat guys.
Tony had Jimmy disposed of, which I had no problem with at the time. Watching it again, however, and seeing that Pussy WAS an informant, is it possible that Jimmy was innocent the entire time?
That would be too bad

No, Jimmy was definitely a rat. Remember that conversation he had with Tony in Tony's basement? Jimmy was trying his best to suck information out of Tony, even going so far as to say something totally ridiculous about some money Tony's crew had supposedly stolen(cant remember exactly what Jimmy said about it but I think it something to the effect of a new fingerprint technique used to lift prints of the bills). As soon as that conversation was over, Tony knew Jimmy was a rat. And also, right before Silvio shot him, he said "Oh Jesus," realizing that they figured out he was talking to the Feds.

The fingerprint thing is suspicious...I forgot about that.

"oh jesus" isnt really an abnormal reaction to getting shot though.

Someone had to have a hand in on Jrs indictment now that i think about it so yeah.
Good riddance to fuckin Jimmy

Well the suspicious thing about "Oh Jesus" is that he said that right after Silvio told him to call for help on his wire. Before he realized they knew he flipped, he shouted something like "I'm a captain you motherfuckers!"

Which episode was he whacked? I forgot.

Season 1 finale

Jimmy Altieri was definitely working for the FBI, and this was confirmed by the words of Agent Skip Lipari (Big Pussy's handler) in Season Two.