The death toll in the Boston Marathon bombings has increased to three people, according to the Boston Police commissioner.
Among the dead was an 8-year-old boy, law enforcement sources told ABC News.
"This cowardly act will not be taken within stride," Boston Police Commissioner Ed Davis said this evening. "We will turn every rock over to find the people who are responsible for this."
At least 133 people were injured, including several children with severe trauma, when bombs exploded almost simultaneously near the marathon finish line, police said.