There was a school shooting and I plan on cutting ties with my friend.
Why do you want to cut ties with your friend?
He didn't do anything to save anyone else including 2 people who are my close friends.
It's terrible to not be supportive to a friend during bad times. You should be helping him instead.
I will go for a walk instead and think about what's important to me.
I think it's the right thing to take that walk and think about it. What happened is truly terrible and your friend most likely is going through a lot of stress.