I tried to write about the Boston Marathon bombings a week ago and got one sentence written before I was stuck; I sat there staring at the screen for some time before I gave up.

This is a very difficult thing to write about in regard to empathy. Of course, we have empathy for the victims. Of course, many write about our common humanity that emerges in these kinds of situations–the heroism, the selflessness. Harder is the question of empathy for the perpetrators. Is it important to understand them and what would cause them to do something so heinous? It feels like doing so is somehow condoning it. “Yes, I understand” usually means, “I sympathize, I can see where you’re coming from, I’d probably do the same in your situation…” Certainly no one means that when they say we should have empathy for the bombers. Can we just write them off as evil? Apparently not, since so many who knew the younger brother, Dzhokhar, cannot reconcile their personal knowledge of him as a nice, normal kid with a terrorist.

A reader sent me a very interesting link to a blog in Boston.com: Reactions to Dzhokhar: Hatred, anger… empathy? I’d recommend checking it out.

But just now, as I was writing this, it became clear to me why I am struggling so with this particular subject. It’s that Dzhokhar himself showed zero empathy to his victims. There are reports from his victims of him looking them in the eye as he set the bomb down and walked away, knowing that he was about to kill them. Fellow humans beings: children, fathers, mothers, friends. He had to completely turn off whatever empathy he normally felt for other people–and people who knew him testify that he was an empathetic, caring guy–to be able to do this. He had to turn off his empathy long before he committed the crime, while he was planning it for however many days. He had to keep it turned off as he was getting himself to the scene, knowing in his head what he intended to do, looking at people as he walked by them, completely dissociating himself from humanity. And then, he had to keep it turned off in the days following, as he saw evidence of the pain and suffering he had caused, as he learned the names of his victims, as he heard about the boy he killed, and the BU student, and the young working woman. He had to keep it turned off as he watched the people he maimed being interviewed on TV, as he watched the families of the victims crying on TV. We all cried as we watched it. How did he not?

How does this happen? How does empathy in a normally empathetic person get so completely turned off? That’s the million dollar question.