>> i felt my heart went down to the floor and rushed 100 miles an hour to my chest. and it was a very, very hard time for his brian, especially. >> brian, the younger son, fell into a deep depression, and drug addiction. he took his own life several years later. >> brian never recuperated from all of these feelings himself. losing his brother was the worst thing that could happen to him. >> the stream keeps coming. >> this year's marathon included runners who were honoring veterans and carlos wanted to support them. but suddenly his mission changed. >> when the first bomb went off, we wasn't too sure about it. when the second bomb went off -- >> something just blew up. >> we pretty much figured out that this was some kind of attack.