The Boston Marathon bombing may be the most videotaped terrorist attack ever.
News crews, spectators and even the runners themselves captured the drama moment-by-moment.
But these images don't just record a moment of tragic history. Investigators are now combing every frame for the smallest clues.
Boston Globe cameraman Steve Silva shot dramatic images as the first bomb exploded. He actually ran into the acrid smoke and flying debris. In his footage, the second blast can be heard less than a block away. Rescue workers pulled away debris to reach the wounded and were greeted by scenes of sheer horror.
INSIDE EDITION's Paul Boyd spoke with Steve Silva.
"As I got closer and I saw a pool of blood, people, bodies lying on top, and saw a man with his legs severed at the knee, I said, 'this is a horrific situation,' " recalled Silva.
Spectator Ryan Hoylme was shooting from a viewing stand across the street and caught the second blast on video.
The explosion and clouds of choking smoke triggered panic as horrified spectators rushed to get away.
Two runners told INSIDE EDITION, "We got thrusted forward and we saw one man in front of us, his legs went up in the air."
The bomb blast was also captured by runner Jennifer Treasy on her cell phone as she raced to the finish line.
One spectator came too close to the action, crossing police lines as the wounded were being treated, and was told by police to leave.
A rescue worker held up a little stars and stripes that was drenched in blood.
Boyd asked Silva, "What do you see when you look at that video now?"
"Just seeing pools of blood on the sidewalk and the faces, unfortunately, on what is usually Boston's best day," said Silva.