When two bombs exploded near the finish line of the Boston Marathon on Monday, many photojournalists were already at the scene, watching as one of the world's best-known running competitions turned to confusion and terror.
"The Marathon finish line scene is usually one of celebration," photographer Ken McGagh told the MetroWest Daily News. "People were initially eerily quiet" after the blasts.
Here, police officers draw their guns as 78-year-old marathon runner Bill Iffrig is knocked to the ground from the force of the first explosion, yards from the finish line on Boylston Street.
Pictures: This Week in Boston
In the wake of the Boston Marathon bombing, the city finds itself in mourning and on high alert while a manhunt ensues.