I don't think Justice should be taken into anyone's hands as the wiseman Harvey Dent had said "You either die a hero or you live long enough to see yourself become the villain."
The system should have punished them accordingly, protecting them from the society by giving them new identities and only imprisoning them until 18 is just one of the worst ways to go about that, it's like catching a terrorist that you know is capable of causing damage that may result in deaths of dozens of people, imprison him for 8 years, listen to his sweet pleas of "I am a changed man!" and let him out.. Only to have him plant a bomb that will kill more people.
In this particular case, the system is fucked up, whichever way you spin it, they've lost their human rights when they abused that 2 year old child, and should have been put down like animals they are.
Disconnect and self destruct, one bullet a time.
