No one had actually believed either side would shoot to kill the other.
At the end of it, they'd been shooting to kill.
Shoot the walls out of the office here to kill you both.
"If you try a break for it, my men will shoot to kill."
This means they can shoot to kill if shot at.
Your client had to shoot to kill in order to get away.
But if it came, he was ready to shoot to kill.
He was always willing and ready to shoot to kill.
But it was just as likely that the guards would shoot to kill.
Shoot to kill anyone or anything that gets in your way.
Idiome