I am not for a self appointed group deciding that someone should be dealt with in a particular manner because they think the courts did not do their job in punishing the offenders, for whatever reason.
I do, however, understand how a distraught parent or spouse might act alone in punishing someone that committed a heinous crime on their loved ones.
When my daughter was threatened, and I percieved her to be in great danger since the police would not do anything about the person that threatened her, I went to his house, pulled him out his front door, and gave him the beating of his life with a pick handle. I then called the police myself, and waited for them. It turned out I was correct in his threats, and his illegal activities. He was arrested for several drug related charges, and possession of several pipe bombs, and material to make more. For some reason the cops thought I just wanted him not to date my daughter, and was telling then things that were not true. My daughter found out about his activities, and when she broke up with him, he kept threatening her, afraid tht she would tell. She was afraid, so she told me. If he would have just left her alone, she would have never said a word. I tried talking to him, but he thought he was so cool and scary that I was nothing to worry about. It was the only way I could get the police involved and prove to him that I was serious that he needed to leave my then 15 year old daughter alone. He lied about his age to her, he was really 20, not the 17 he had told her.
No charges were pressed against me, but if they had been, I was prepared to accept the consequences. Sometimes you just have to do what you feel is right, legal or not.