This argument has always been strange to me. Killing, especially guys in witness protection program is bad for business. Why do the feds leave them alone to begin with if they can put heat on them? Why not squash the whole thing if they have the resources to do it? Is it corruption or some human phenomena, that a dead witness makes the agent put down his newspaper and start investigating? I never saw much sense in the explanations that it's good to keep crime going to keep up the Gambino squad budget.