Does the failure of the law mean we should take the law into our own hands? The legal system has many more resources than we do as individuals to find out who is guilty and what the appropriate punishment is. Our judgement may be wrong. We may not foresee the repercussions of our actions. There is a risk that if we take the law into our own hands we will cause more harm than good.
Timothy McVeigh, when he blew up the government building in Oklahoma was taking justice in his own hands, apparently to avenge the fire at Waco Texas which occurred after the FBI moved in. The result was clearly not justice and the death of many innocent people including children.
Orthodox Yigal Amir shot Yitzhak Rabin to stop him from turning land he believed God had promised to the Jews, over to the Arabs. This murder did not accomplish his objective, if anything it created sympathy for those who advocated giving land to the Arabs and hostility to those who shared his views about holding on to the Biblical land of Israel. His murder of Rabin created a great deal of hostility toward orthodox Jews from fellow Jews in Israel.
Although I believe it is everyone's duty to help make the world a just place, I also believe that we have to be very careful not to commit injustice in our effort to promote justice. Many people are actively involved in causes because they want to make the world a better place, but actually are making the world a worse place because they didn't carefully study the situation before they started advocating a position. Part of our responsibility is to be aware and to study a situation objectively before we actively take sides.