During a meeting with the other crime family Dons to establish peace, Vito realizes that Barzini masterminded Sonny's murder. After Michael returns from Sicily, he assumes Sonny's place as Vito's heir apparent. Vito and Michael secretly continue Sonny's plot to wipe out the other New York Dons to avenge Sonny's death and purge their rivals once and for all. After Vito dies in 1955 from a heart attack, Michael has the other New York Dons murdered, including Barzini, who is shot twice in the back on the steps of a courthouse in broad daylight. Michael informs Carlo that the rival Dons have been killed and coerces Carlo's confession for his part in arranging Sonny's murder. Carlo admits Barzini was the mastermind. On Michael's orders, Clemenza garrotes Carlo to death. In a single strike, the Corleones become the most powerful crime family in the country.