This is a no win situation. A 16 year old kid with clear mental issues, bad back ground, and life makes a decision which takes the lives of two humans. You can't bring them back but you also don't bring them back by letting this person rot in jail. 

I've also been a victim of a gun crime watching someone I love shot and killed in front of me. I could sit back and be angry my whole life but I choose empathy. In my case the killer had a similar back ground. He needs to serve time for sure, but I'd never expect him to be in jail for life. People need to be given a second chance. 

I could tell you of another story where someone was given a second chance and now counsels youth offenders and trouble kids into making better decisions. You never know the path these things take but I'll choose empathy and hope over cynicism any day.