A question on moral stance perhaps.?

My opinion is, Person 2 preempted the rightful duty of the court to try and sentence this man. I don't think any of us want to exist in a society where each individual is judge, jury, and executioner. This is obviously an exceptional cirstance, and thus, one in which principle and not emotion rules the day. I feel Person 2 should be tried for murder, but with as lenient of a sentence as the law would allow for such a crime. It must be punished, but I feel leniency should be applied.