I had a similar problem when my son was doing his GCSEs a few years ago - he received death threats from a former 'friend' who thought that he was coming on to his ex girlfriend. The boy had a drug problem at this stage, having been expelled from school and as his dad was a reasonably well know South London 'gangster' we were really concerned as we thought he would have the means to carry out his threats. The school were great, with some of the teachers giving up personal time to escort my son to and from the bus stop etc after school, however we went to school one day for a meeting about it and while my son went outside to catch up with his friends the boy turned up unexpectedly and beat the s**t out of my son. His friends tried to help and one ran home to get a neighbours dog. My son kind of let him get on with it and didn't put up much of a fight as he thought it was something the guy needed to get out of his system, and sure enough he left him alone after that, his anger seemed to be depleted. It was a horrible time for all of us, but I think we were more worried than him. I'm not saying your sons should take a beating, but maybe them being away will give the guy some time to calm down - it is often bravado. The boy contacted my son about a year later to say that part of the problem was that he was jealous that my son had a home, and people who care about him, whereas he was left by himself most of the time. It did have an impact on his exams though and he did under perform, so it's important that you don't let that happen. I hope it all sorts itself out.