You helped though. Without you he wouldn't even be able to be killed.
You're judging, not helping to kill or whatever.
It's your job, you have spent like 8 years learning specific stuff to get this specific job, not including normal school and college.
It's his fault for doing a crime anyway. If he didn't understand the fact that he will be punished he wouldn't have done it.
Anyhow, 9 bullets, a mag and a handgun cost way less than housing 9 immates for periods longer than 40 years.