I was on the outskirts of New York City on September 11, 2001 when I got the news that an airplane had crashed into the World Trade Center. My twin brother was in his office on the 85th floor. I tried to call him but couldn’t get through. 

The plane hit eight floors above my brother’s office. He ran down the stairs, stepping outside minutes before the building collapsed behind him. He is alive. Thousands are not. That day, I decided to dedicate my life to understanding what motivates violence. 

Twenty years ago, on Sept. 11, 2001, the world was shocked at the coordinated attacks on the World Trade Center and the Pentagon, resulting in the deaths of nearly 3,000 people.