What am I supposed to feel?

Last night, my wife logged onto Facebook and read that Osama Bin Ladin had been killed as a result of a military action by the U.S. in Pakistan. The news has been saying that this is day we'll remember forever, like where we were when we heard about the planes hitting the towers almost 10 years ago. But is this something I want to remember?
Bin Laden lived a violent life, and his actions led to the deaths of thousands of people in multiple countries from various religious and ethnic backgrounds. The lives of others were expendable to him and he had been declared the enemy of nearly every established government in the world. The world is definitely a safer place without him gone. Yet I cannot help but wonder why we are celebrating someone's death to such a degree. The ending of a life is something very saddening to me, whether it is because their death was a tragedy, or because it was necessary.
I am not trying to say that I am not sad that he is dead. I am saddened because this is what had to happen. I feel this way anytime anyone dies who "deserves it." Death for someone who is in that state holds no hope. A person who dies with their heart so firmly rooted in evil is truly lost. And so even though it was necessary, I regret that it was the last option.
In a nutshell, I'm conflicted. I wonder if I'm supposed to feel compassion towards a man whose actions have destroyed innumerable lives, lives of people I know and feel for. I had family in New York who lost friends and loved ones on September 11th, 2001. I felt the fear that war would engulf us and my friends and I might be drafted to fight. I know soldiers who've served in Iraq and Afghanistan over the last decade. I know that Bin Laden's actions have caused great suffering and pain to these people. I am only lamenting that ending another man's life was the only solution to stop him from continuing to hurt others. Kill to prevent killing is a concept I've never been fully comfortable with.
In short (too late), I am only left not knowing how to react to the news. His death is cause for both joy and sadness, and I am finding it hard to choose which to feel. I'll definitely remember it, though, even though I don't really want to.