I don't think that's true. They also killed numerous politicians, people in the financial world, other criminals, regular people, ... And what to think of all the bystanders who were hit by bullets or explosions that were meant for somebody else. Imagine walking on a street, a mafioso crosses you, and just at that moment, other mafiosi try to shoot the first guy. They kill him, but unfortunately they also kill you.
Those things happened a lot...