Terror at Boston Marathon: 3 dead, 154 wounded as witnesses describe horror

(CNN) — Investigators are pleading for help in hunting down those responsible for a pair of bombings that left a gruesome scene at the Boston Marathon.

The blasts, which killed an 8-year-old boy and two other people, marked a grotesque end to what should have been a celebration of triumph.

One man’s legs were instantly blown off, yet he kept trying to stand up.

Exhausted marathoners had to muscle the energy to flee the bloody scene.

And more than 150 people were hospitalized, some in critical condition.

“No piece of information or detail is too small,” the FBI Boston Division said, asking the public for any information or images that might provide clues. Among other things, authorities are asking people to check their cell phone cameras for possible leads, said Juliette Kayyem, a former U.S. assistant secretary for homeland security.

Investigators don’t know the motive for the bombings and don’t have a specific suspect, nor have they found any surveillance video showing the bombs being placed, a law enforcement source told CNN on Tuesday.

A day after the bombings, as Pope Francis told Bostonians to “combat evil with good” and runners in Atlanta staged a silent run to commemorate the victims, Americans alternately mourned and nervously wondered who was behind the violence.