I disagree with people arguing that only some crimes should grant trial as adult - Either you're trialed as an adult for ALL Crimes or you're trialed as a child/adolescent and given proper measures. I think most people forget that most punishment methods against minors involves a correction facility and in many ways it is as bad as a prison and limits your freedom. As a general rule, I think between 15-16 years old is fine to be trialed as an adult. The main argument to support less bad punishment for minors and young adults, as I learned in class, is that the younger someone is, specially highly influenciable people like teens, the easier it will be to rehabilitate them.
Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you