We get that Frank Pentangelli turns informer because he thinks Michael betrayed him and probably feels he's a dead man either way - Moe Greene wants him dead, so does Mike, so who else is he going to turn to?

But what about Willi Cicci? He was one of Michael's inner circle guys, at least at the end of GF I, I mean he was trusted enough with whacking a Five Families boss. He was part of Sonny's crew and seemed line one of his main guys as well (In almost scene where Sonny is Acting Boss, Willi is with him as both bodyguard and enforcer)...His turning witness was surprising.