The ones that I've taught that went on to kill have been no surprise. Total self-preservation in all things and quick to react with violence to any perceived disrespect.
One of them was trying to impress fellow gang members and picked a victim at random to hit with machete. I remember him as a kid, knotted up inside. I sat with him one afternoon and chatted to calm him after he had trashed a classroom and remember that at the time I just wished someone had intervened earlier in his young life.
Another was a big swaggering lad who was a one-punch killer. I don't think it was intentional with him, but he had a really bad attitude and I can imagine how it happened.
Both of those guys would probably have grown out of it given a while to mature a bit, but unfortunately for them and their victims, it didn't happen.
A couple grew up to seriously sexually abuse children. I definitely wasn't surprised with one having taught him for a couple of years. I'm glad he was caught.
I do scan local media occasionally and there are a few struggling to stay the right side of the law. Usually their offences make sense, knowing what they used to be like. Again, with time and maturity there are fewer of these.
There have been a few comedy moments, like when one guy was being sought by police for attacking a random stranger and phoned in on the number given to argue that yes he had punched and kicked him, but the bloke had said something he didn't like.
On the positive side, many, many kids have gone through seriously messed up times and have never made headlines anywhere. Hopefully being able to read and write and having learned some anger management from a teacher who wanted them to be their best has helped them live ordinary, uneventful lives.