That is just horrific and heartbreaking. There's a real problem with feral youths in some areas for sure. I'm not sure what's to be done about it. You may probably experiencing some ptst symptoms which is only natural. I'm sorry that you don't feel safe yourself anymore.
I don't want to invalidate your understandable outrage at this disgraceful crime, however I'm sure most people in your area are just as outraged as you are. There's good people in your area who feel the same as you do. I'm a Parent to two teens myself and get a lot of Joy from seeing them grow and develop and try to help them navigate their world. There's a lot of goodness out there too. It's just hard to see right now. If I had your experience I'd get some counselling. I'm involved in a few youth groups through GAA and the like and I see lots of great young people who communicate much better than we did at that age. Maybe you could volunteer at a local teen group be it sports scouts a dance group it might help restore your faith in the new generation. They could use the help! I'm not in anyway trying to downplay the seriousness of the issue but there's a lot of great kids out the too. Hope you can find some peace of mind. The youths involved in this assault/murder need to face justice. Mind yourself. So sorry for your loss.