One of the questions from the audience at the Yum Center in May 2013 came from a person who said, plainly, that they were having trouble forgiving the perpetrators of the Boston Marathon bombings, which had happened a little over a month earlier. The Dalai Lama's answer separated two things people often run together. In practical terms, he said, the people who do such acts have to be brought to justice. He added that he is a longstanding signatory of the Amnesty International campaign to abolish the death penalty, and that the work of forgiveness is to distinguish the action from the agent who carried it out. The agent is also a human being.
The distinction is older than the occasion. The classical source the Dalai Lama draws on is the sixth chapter of Śāntideva's Bodhicaryāvatāra, the chapter on patience. Śāntideva argues there that anger at a person who has harmed us is misplaced, because the person acted under the compulsion of mental afflictions, and the afflictions are the proper object of any anger that needs an object. Tsongkhapa makes the same argument in the patience section of the Lamrim Chenmo. The Dalai Lama's own commentary on the Śāntideva text is Healing Anger, which walks through the passage in detail.
He gave the answer in front of fourteen thousand people, to a question from someone in real difficulty. He did not soften the practical claim. He did not suggest justice should be set aside, or that the feeling of difficulty was wrong to have. He moved the question one step inward, to where the practice has to be done.
The Boston bombings killed three people at the finish line and injured several hundred more, some of whom lost limbs. The first anniversary was almost a year away when the question was asked. The distinction the Dalai Lama drew is correct and very hard to live by.