Police on Boston bombings: 'This cowardly act will not be taken in stride'

BOSTON (CNN) -- Federal agents and state and local police have launched a massive investigation into the twin bombings at the Boston Marathon that killed three people, including an 8-year-old boy, and left more than 170 others injured.

The bombings turned a celebration into a bloody scene of terror and destruction.

"This will be a combined federal, state and local effort. It will be an ongoing investigation. It is a criminal investigation. The FBI is bringing substantial -- very, very substantial -- federal resources to bear along with our federal partners. The ATF is well represented here,” FBI agent Rick DesLauriers said.

Describing it as a "criminal investigation" that is also "a potential terrorist investigation," DesLauriers said the FBI was declaring federal jurisdiction over the matter through the Boston Joint Terrorism Task Force.

They are looking for clues and evidence that might lead them to the bomber or bombers.

"This cowardly act will not be taken in stride. We will turn every rock over to find the people responsible for this,” Boston Police Commissioner Ed Davis said.

Authorities said Boston will be largely open for business on Tuesday, but heavily armed police will be out in force, bags will be searched on the ­MBTA, and the area around Copley Square will remain a crime scene, closed to the public.

Two people were initially killed in the blasts that occurred shortly before 3 p.m. ET Monday, and a third person died hours later, Davis told reporters Monday night.

The total of injured has risen to 144 people, officials at Boston area hospitals said. At least 17 of them were listed in critical condition and 25 in serious condition. At least eight of the patients are children.

Doctors reported they were "pulling ball-bearings out of people" in the emergency rooms, suggesting that the bombs were designed to propel shrapnel, a terrorism expert told CNN.

President Barack Obama pledged the full resources of the federal government in helping Boston and in investigating the bombings. The FBI quickly took over the investigation.

“The American people will say a prayer for Boston tonight,” Obama said in televised remarks. The president said he had spoken with congressional leaders and that all were united in dealing with the tragedy.

Obama cautioned that authorities were still investigating and that people should not jump to any conclusions before all of the facts are learned.

“But make no mistake,” Obama said. “We will get to the bottom of this and we will find out who did this. We’ll find out why they did this.”

Individuals and groups responsible “will feel the full weight of justice,” the president said.“We will find out who this and we will hold them accountable.”

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Officials began questioning at least one person in connection with the explosions.

The terrorist attack, near the marathon's finish line, triggered widespread screaming and chaos, shattered windows and barricades and sent smoke billowing into the air at Copley Square.

The blasts were about 50 to 100 yards apart, officials said, on a stretch of the marathon course lined with spectators cheering runners through the final yards of a 26-mile, 385-yard endurance feat.

"It felt like a huge cannon," a witness told CNN about one of the blasts.

Photos from the scene showed people being carried away on stretchers. One man in a wheelchair had blood all over his face and legs.

Federal authorities are classifying the bombings as a terrorist attack, but it's not clear whether the origin was domestic or foreign, a federal law enforcement official with knowledge of the investigation said.

A federal law enforcement official told CNN that both bombs were small, and initial tests showed no C-4 or other high-grade explosive material, suggesting that the packages used in the attack were crude explosive devices.

A federal law enforcement official said authorities were questioning a Saudi national who was taken to a Boston hospital with injuries. The person was not identified as a suspect, however.

The official also said authorities are also “desperately seeking” a Penske rental truck seen leaving the race site. They further believe the explosive devices were small bombs placed in small receptacles and that at least one was detonated in a nearby trash can.

The police chief urged people to stay indoors and not congregate in large groups, casting an ominous pall over what should have been a celebratory scene after the annual running of marathon. About 27,000 runners took part in the 26.2-mile race, one of the world's premier marathons.

Authorities in Boston found at least one other explosive device that they were dismantling, Boston Police Commissioner Ed Davis said. Rep. Bill Keating of Massachusetts, meanwhile, said there were two more found.

One unexploded device was found at a hotel on Boylston Street near the bomb site and another unexploded device was found at an undisclosed location, Keating, a Democrat and member of the House Homeland Security committee, said.

It was unclear who may have planted the marathon bombs. There were no credible threats before the race, a state government official said.

There is no suspect in custody, but many people are being questioned, Davis said.