I totally agree with your son. Let the mom's handle it if that's what needs to happen. If not, let it drop.
I also agree it was likely a boneheaded move. I was a boy. I did some dumb things. I grew up. It's part of growing up.
If you do decide you feel amends need to be made, handle it with his mom and keep that trust with your son. Your son is not stupid about this.
Your H cares, BTW. His way of caring and showing that care is different, but I read in your post he does care. And not just about retribution or the money, although that seems important to him.
My $0.02 anyway. AJ
"Our lives begin to end the day we become silent about things that matter" MLK Put the glass down... "Yesterday I was clever so I wanted to change the world Today I am wise, so I am changing myself."