Brazilian Teen killed 12

A 16 year old Brazilian teenager admitted to killing 12 people most out of rage. How is it that people get disturbed at such a young age? Its becoming more and more common, people under 18 committing ruthless acts of murder, and not that its ok if you're older but its amazing what some people are capable of doing. And it took 12 murders before the boy was caught? Don't mean to discredit Brazilian police but how did a 16 year old manage to get away with 12 murders before being caught? I'm astonished.