I believe he was eventually convicted of all three murders as well as a score of others.
Dennis Allen was a fucken nutjob. He started informing on rivals pretty early in his career. In a sense, the extended Pettingill clan served as his "enforcers", but he always had a bunch of hanger-ons around him (Not the Flemington crew, they mainly stuck to bank robberies, but I've seen people include them with Allen before. Allen was a drug dealer, first and primarily, before his other rackets). In latter day interviews, Jason Ryan admitted to being party to some of Allen's violence, as young as he was (just what Ryan has said, not sure how much credence to put in to that).
As far as the Angels are concerned, IIRC Anton Kenny was known as an informer himself, and was no longer affiliated with the local chapter by the time of his murder.