Three Killed, 176 Injured in Explosions at Boston Marathon Finish Line

UPDATE: A total of 17 people remained in a critical condition on Tuesday, a day after two bombs killed three people and injured 176 at the finish line of the Boston Marathon.

Boston Police Commissioner Ed Davis confirmed that no one has been taken into custody since the sickening attack. No additional explosive devices were found on the scene, Massachesettes Governor Deval Patrick said during the same briefing.

Defense Secretary Chuck Hagel described the outrage as "a cruel act of terror" and vowed that those responsible will be brought to justice.

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Two people were killed and more than 20 were injured when explosions erupted near the finish line at the Boston Marathon on Monday.

The explosions occurred about three hours after the winners crossed the finish line. First responders and race officials dashed on to the course to carry away the injured. Blood-soaked spectators were treated in the medical tents that were supposed to care for fatigued runners.

The Boston Police Department confirmed that they were looking into an explosion, but had no further comment. Officials could not immediately say the exact number or degree of injuries.

Initial reports say a loud explosion was heard on the north side of Boylston Street near the finish line, with a second explosion several seconds later.

"Somebody's leg flew by my head," a spectator, who gave his name as John Ross, told the Boston Herald. "I gave my belt to stop the blood."

Boston Herald reporter Chris Cassidy, who was running in the marathon, told the newspaper: "I saw two explosions. The first one was beyond the finish line. I heard a loud bang and I saw smoke rising. I kept running and I heard behind me a loud bang. It looked like it was in a trash can or something. There are people who have been hit with debris, people with bloody foreheads."

The Boston Marathon is one of track’s most storied events, established in 1897 and one of the six World Marathon Majors. The event typically attracts an estimated 500,000 spectators and requires certain qualifying times for runners to compete.