Deadly terrorist attack strikes Boston Marathon's finish line

At least three people died and scores were injured Monday after two bombs detonated in a terrorist attack at the annual Boston Marathon. 

President Obama, speaking to the nation Monday evening, vowed to bring the perpetrators of the bombing to justice. 

“We still do not know who did this or why, and people should not jump to conclusions before we have all the facts,” Obama said at the White House. 

“But make no mistake, we will get to the bottom of this and we will find out who did this. We’ll find out why they did this. Any responsible individuals, any responsible groups will feel the full weight of justice.”

Obama was updated overnight “on the ongoing response efforts and investigation into the explosions in Boston, including the continuing federal support for those activities,” a White House official said. 

“The President made clear that he expects to be kept up to date on any developments and directed his team to make sure that all federal resources that can support these efforts, including the investigation being led by the FBI, be made available,” the official added.

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Obama will receive another briefing from FBI Director Robert Mueller and Assistant for Homeland Security and Counterterrorism Lisa Monaco on Tuesday morning.

The blasts prompted the Secret Service to extend the security perimeter outside the White House, while police heightened security in Washington, D.C., New York and other major U.S. cities. 

Speaker John Boehner (R-Ohio) on Monday evening led the House, which was in the midst of a series of votes, in a moment of silence in honor of the victims.

While the president did not specifically describe the blasts as terrorism, shortly after he spoke the White House said it is treating the bombing as an “act of terror.” It’s not known if a foreign or domestic group is responsible. 

“Any event with multiple explosive devices — as this appears to be — is clearly an act of terror, and will be approached as an act of terror,” said a White House official. “However, we don’t yet know who carried out this attack, and a thorough investigation will have to determine whether it was planned and carried out by a terrorist group, foreign or domestic.”

The bombing was the first terror attack on U.S. soil since 13 people were killed and dozens wounded in a November 2009 shooting spree at Fort Hood, Texas. 

“We’re still in the investigations stage at this point, but I just want to reiterate we will find out who did this and hold them accountable,” Obama said.

The president said he was “supremely confident Bostonians will pull together, take care of each other and move forward — as one proud city.”

Rep. Michael Capuano (D-Mass.) spoke briefly before the moment of silence in the House, describing those responsible as “evil” and noting the bombings likely affected several nations around the world.

“By the way, this event was not just a Boston event,” Capuano said. “The Boston Marathon is an international event that draws people from around the world, and I would be shocked if many of the people who were injured today were not from Massachusetts.”

The two explosions occurred 50 to 100 yards apart from each other near the finish line at 2:50 p.m., Boston Police Commissioner Ed Davis said at a press conference. 

Police did not have a suspect in custody, he said. 

“There is no suspect in custody,” Davis said. “We’re questioning many people but there is no one in custody at this time.”

NBC News reported that small home-made bombs were responsible for the blasts. Intelligence officials said two more explosive devices were found, according to The Associated Press.  Boston police said this evening that no additional explosive devices had been found. 

The AP reported early Monday evening that more than 100 people were injured in the two blasts. 

But Davis said police were not ready to give a count of how many were injured or killed. 

“We don’t have the number of casualties at this point in time,” Davis said. “This is very early in this investigation.”

Officials declined further comment on the investigation.

Local station WBZ-TV reported that police searched an apartment in Revere, Mass., a Boston suburb, in connection with their investigation. Massachusetts State Police said a search warrant was served but did not provide additional details, according to the report.

Obama was first notified about the incident by Homeland Security adviser Lisa Monaco and staffers at 3 p.m., according to the White House. 

The president called Massachusetts Gov. Deval Patrick (D) and Boston Mayor Tom Menino “to express his concern for those who were injured and to make clear that his administration is ready to provide needed support as they respond to the incident,” according to the White House.

Obama was briefed by Federal Bureau of Investigations Director Robert Mueller and Homeland Security Secretary Janet Napolitano about the investigations of the explosions Monday afternoon. 

He briefed Boehner at about 5:30 p.m. 

Security immediately tightened around the White House at around 4 p.m., with tourists being moved off Pennsylvania Avenue and into a nearby park.

“Out of an abundance of caution, we have expanded our security perimeter at the White House complex. It is not unusual to expand or contract these security perimeters,” Secret Service spokesman Ed Donovan said.

Police in Washington told NBC News that they had “heightened security” in the nation’s capital. The D.C. Metrorail subway system increased police patrols on their lines.

In Boston, local television feeds showed a chaotic scene at the finish line, with emergency personnel seeking to attend to the injured.

The Boston blasts happened roughly three hours after the marathon winners passed the finish line. The annual race takes place every Patriots’ Day, a civic holiday in Massachusetts held on the third Monday of each April commemorating the first battles of the American Revolution.

The explosions were reportedly heard seconds apart from each other. The Lenox Hotel in Boston was evacuated in response to the blasts, the Boston Globe reported.

A special mile marker at this year’s marathon was dedicated to the victims of the shooting massacre at Sandy Hook Elementary School in Newtown, Conn., in December. The mile marker hung at the 26th mile of the marathon. The explosions happened near the finish line of the 26.2 mile route.

Vice President Biden was on a conference call when news broke about the explosion.

“Our prayers are with those people in Boston who have suffered injuries,” Biden said. “I don’t know how many there are.”

Maine Sens. Susan Collins (R) and Angus King (I) issued a joint statement that said the bombings had the “hallmarks of a terrorist attack.”

“As members of the Senate Intelligence Committee, we will be continually updated of the situation. In the meantime, initial press reports that multiple improvised explosive devices may have been involved at this high profile national event bear the hallmarks of a terrorist attack,” the two senators said. 

“We stand united as Americans in our unfaltering support of one another.”

— Justin Sink, Jordy Yager and Pete Kasperowicz contributed.

—This story was posted at 3:05 p.m. and has been updated.