Jimmy was already in the police books for conspiracy and then he gets caught with pistols and AK47's, illegal gambling too and as Tony puts it he managed to escape those charges on low bail and out in time for dinner.. Jimmy says to Tony "you got a problem" , he says "yeah I'm working on it" to which Jimmy replies "working on what" .. if you think by those actions and conversation he isn't a rat then you need your head examined lmao