Bombs at marathon leave 3 dead in Boston

The blasts threw people to the ground. Boston Police Commissioner Ed Davis said Monday night that the death toll had risen to three. Scores were injured at the scene.

One of the dead was an 8-year-old boy, according to a state law enforcement source.

Hospitals reported at least 141 people are being treated, with at least 17 of them in critical condition and 25 in serious condition. At least eight of the patients are children.

At least 10 people injured had limbs amputated, according to a terrorism expert briefed on the investigation, according to CNN.

Doctors are "pulling ball bearings out of people in the emergency room," the expert said, suggesting the bombs were designed to propel shrapnel.

"Any responsible individuals, any responsible groups, will feel the full weight of justice," President Barack Obama vowed.

Boston "is a tough and resilient town," he said, adding that Americans will stand by Bostonians "every single step of the way."

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