Vigilantes DO NOT administer justice. A murder of a murderer is murder. The state is the God-given authority on that matter. Democracies and Tyrannies alike. And don't give me the lines about "would you kill Hitler if you had the chance"? or that war is somehow murder. Wars are waged by governments who have the authority to bear the sword against what is wrong... Read Romans 13:
Let every person be subject to the governing authorities. For there is no authority except from God, and those that exist have been instituted by God. 2 Therefore whoever resists the authorities resists what God has appointed, and those who resist will incur judgment. 3 For rulers are not a terror to good conduct, but to bad. Would you have no fear of the one who is in authority? Then do what is good, and you will receive his approval, 4 for he is God’s servant for your good. But if you do wrong, be afraid, for he does not bear the sword in vain. For he is the servant of God, an avenger who carries out God’s wrath on the wrongdoer.
The Holy Bible : English Standard Version. (Wheaton: Standard Bible Society, 2001), Ro 13:1-4.
Paul wrote this when Nero was burning Christians as torches to light his garden. Deal with the tension, believer. Governments do not always have biblically moral policies. And in a perfect world, our government should outlaw the brutal murder of unborn children. But it does not. And had it acted on late-term abortion provider George Tiller, it would have indeed been justice. But one angry anti-government madman is not justice. It is further injustice. It hurts the peaceful and prayerful pro-life cause more than we can imagine.
Christians, let's make sure we understand justice. Only Jesus will dispense it in eternity (Read Acts 17:30-31). And it is an imperfect and rare commodity until then. When we understand that only God gives justice, we do well. When we think that humans will always do it, we make a HUGE MISTAKE. Fallen humanity cannot really understand justice. Even the best judge is born a wicked sinner who rages against God. Even a Christian involved in the legal system or law enforcement still struggles with a selfish human nature. Let's understand that. And don't let ourselves think that justice was somehow served. It wasn't...
Evil men do not understand justice,
but those who seek the Lord understand it completely.
The Holy Bible : English Standard Version. (Wheaton: Standard Bible Society, 2001), Pr 28:5.