Well, I think that we need to forgive what was done to us, but never forget. We should also impose punishment for what was done. Crimes cannot go unpunished, including mass murder. I don't believe that the Bible tells us to let this sort of thing slide though.
I do believe that we should be praying for our enemies. I've been praying for them since this happened. I've prayed that they will see the error of their ways and come to know God in the form of Christ Jesus. If they repent, they will join other Christians in the kingdom of heaven. However, accepting God will not protect them from earthly punishment. The Bible says to pray for your enemies (anyone who you are angry with or who is angry with you) because it will heap coals on their heads. The coals refer to coals used to forge metal, essentially telling us that our prayers can bring about change in our enemies.
You guys can flame me all you want, or call me stupid or whatever. However, I believe that the best thing I can be doing is praying for these people, and of course our country and all who were affected by this tradegy.
Ryan