This isn’t a “Is killing a person that insulted you right or wrong?” moral conundrum, it’s a “If you could kill Hitler after he had started exterminating people, would that be right or wrong?” moral conundrum.
Most people who would say “it’s the wrong thing to do” for the first one would say “it’s the right thing to do” for the second.
Mind you, the really right thing to do on the situation with this CEO would have been for the State to do its fucking job and protect the people from mass murderers like him, but it refuse to do so, hence here we are in a bad situation.
It’s a corrupt system.