Legato killed himself, Legato put is his head pactically in front of the barrel of the gun and he was also about to kill Vash's friends. And given Legato's mental powers, even though Vash pulled the trigger, I am not sure Vash was the one who willed his finger to pull the trigger.
Also, in his 130 years of living, he had not killed even one person.
Now stop trying to change the subject of this thread. If you want a thread about Trigun, just start one about it.