According to former Mullen boss Patrick "Pat" Nee, McGonagle ambushed and murdered O'Sullivan on the assumption he was the one responsible for his brother's killing. Bulger, realizing he was on the losing side, secretly approached Howie Winter, the leader of the Winter Hill Gang, and claimed he could end the war by murdering the Killeen leadership. Shortly thereafter, on May 13, 1972, Donald Killeen was gunned down outside his home in the suburb of Framingham. Nee disputes this, claiming that Killeen was murdered by Mullen enforcers James Mantville and Tommy King, not Bulger.