All good advice. The best is to tell him you love him and if he ever wants to talk about this, you will be there to listen, any time.
If your son actually knew the young man and wants to share his feeling with the family, he could write them a note.
If he did not know the young man, he could send a condolence card and participate in any memorial that is organized.
I know at our daughters HS a few students died or were killed in accidents and trees were planted on campus. The Entire Band actually performed at one memorial service. (very touching)
This is a time to talk about how things happen for no reason. But we learn from this. We learn to be our best, to always work towards our goals. To follow our passions, just like this young man was doing.
Just be there to listen, but do not go on and on about this. He will let you know when he is ready to talk about it. He may want to be with classmates or band mates and that is natural and yes, I am sure Counselors will be up at the school to help.
I am sorry for your community and the young mans family.