Might get flamed for this, but I’ve done voluntary youth work in a fairly rough inner city for over 20 years. You need to find a way to seriously punish the behaviour without pushing him away.
If his behaviour is at a point where incidents like this are happening Then the chances are he and his friend have been involved in antisocial behaviour for a while.
My approach, if this was my DC, would ils be to come down on it like an absolute ton of bricks, whilst keeping him close.
You need to speak to the friends parents to get an idea of how they handling it to know whether they’re going to take it seriously or not. If not, that has to be the end of the friendship.
If possible can you also speak to the police officer again to understand if this is a one off incident or if your son is been involved in trouble previously or is known to them?
Your son needs a very clear message you know what he has been up to and he can’t hide it any more. If he’s in over his ahead he might be relieved, if he’s a ring leader he will be more angry at being caught out.
Either way he needs to know that his stupidity could have ruined his life, if the police had pursued it he could have limited his education options and career choices, if the man had been seriously injured he could have been locked up. How would he feel if he had to go to court and it was in the local papers, his mates might think it’s hilarious, but his grandparents, mates friends and teachers all knowing? Not to mention that he could have injured or killed the guy, and for what? He could have left kids without a father, how would he feel if someone attacked you?
Immediate consequences would be no phone no Xbox no money no going out the house without a parent for a decent period.
I’d also make it clear that Christmas presents are contingent on his behaviour between now and then.
I would make his only opportunity to get out of the house some structured organised activities. Martial arts, army cadets or sea cadets, boxing. Something that will give him a physical outlet whilst at the same time instilling self-discipline.
If he complies then he can earn back some freedoms and trust, but he has to work hard over a period to earn it back.
At the same time organise some 1:1 time with you, some activities like Go-ape, climbing, BMX track racing, some volunteering you can do together, a city break somewhere he is interested in, surfing lessons. Things that are a real treat, that he needs you to do with him, and will make him feel close to you and give him a sense of achievement. Don’t mention the behaviour or the incident during this time unless he opens up.
He needs to see that there are clear and uncomfortable consequences to his actions, but at the same time you love him, want to spend time with him and haven’t written him off as a ‘bad kid’