‘Act Of Terrorism’ Was ‘Heinous And Cowardly,’ Obama Says

Boston Explosions Update at 12:40 p.m. ET. Where Things Stand.   DEATHS, INJURIES: Three people were killed and at least 176 were injured, according to Boston Police. At least 17 of the wounded were critically injured.

    INVESTIGATION: Authorities searched an apartment in the Boston suburb of Revere late Monday. They left with some bags. There have been no arrests reported and officials aren't commenting on whether anyone is or isn't in custody. A doctor who treated victims says an X-ray indicated that BBs or ball bearings may have been packed into the explosives. Massachusetts Gov. Deval Patrick (D) said that all parcels left at the scene have now been examined and no additional bombs were found. The AP and CBS are reporting they've been told by informed sources that "pressure cooker bombs" were used.

 President Obama told reporters that it's clear this was an "act of terrorism," but that it's not known yet whether it was the act of an individual or a group, and whether it was foreign- or domestic-related.

SECURITY: As Boston and other major cities across the nation and around the world keep their police on alert, there's particular concern in London — which hosts former Prime Minister Margaret Thatcher's funeral on Wednesday and a major marathon next Sunday. "British officials on Tuesday urged a review of security measures," The New York Times says. Meanwhile, FBI Special Agent in Charge Rick DesLauriers said Tuesday that there are "no additional threats" in Boston.

Update at 12:40 p.m. ET. "Pressure Cooker" Bombs?

 A "person briefed on the probe" tells The Associated Press that the bombs were "pressure cookers with metal [and] ball bearings" packed inside. It isn't know yet what was used to set off the explosions, the AP reports.

   CBS says that "A law enforcement source told CBS News that one of the explosive devices appears to have been placed in a metal pressure cooker (a metal kitchen pot with a locked down top) which had been placed in a black nylon bag or backpack. Investigators also found pieces of an electronic circuit board possibly indicating a timer was used in the detonation of the bomb.

    "A law enforcement official told CBS News that the two bombs that exploded were made to look like discarded property. It is still unknown if one or both bombs were in garbage cans. One may have been on the sidewalk."

According to a 2004 Department of Homeland Security memo, "these bombs are made by placing TNT or other explosives in a pressure cooker and attaching a blasting cap at the top of the pressure cooker."

NPR has not independently confirmed that authorities suspect pressure cooker bombs were used.

As we said when the day began: We will focus on news being reported by NPR, other news outlets with expertise and statements from authorities in position to know what's going on. And if some of that information turns out to be wrong, we'll update.

Update at 11:35 a.m. ET. This "Act Of Terrorism" Was "Heinous And Cowardly," Obama Says:

Speaking at the White House, the president just said that "given what we now know about what took place, the FBI is investigating it as an act of terrorism." What isn't known, he said, is whether it was the act of an individual or a group, and whether it was foreign- or domestic-related.

The way people at the marathon responded and helped each other, the president added, shows that "the American people refuse to be terrorized" even by such a "heinous and cowardly act."

    INVESTIGATION: Authorities searched an apartment in the Boston suburb of Revere late Monday. They left with some bags. There have been no arrests reported and officials aren't commenting on whether anyone is or isn't in custody. A doctor who treated victims says an X-ray indicated that BBs or ball bearings may have been packed into the explosives. Massachusetts Gov. Deval Patrick (D) said that all parcels left at the scene have now been examined and no additional bombs were found.

    SECURITY: As Boston and other major cities across the nation and around the world keep their police on alert, there's particular concern in London — which hosts former Prime Minister Margaret Thatcher's funeral on Wednesday and a major marathon next Sunday. "British officials on Tuesday urged a review of security measures," The New York Times says. Meanwhile, FBI Special Agent in Charge Rick DesLauriers said Tuesday that there are "no known additional threats" in Boston.

Update at 10:10 a.m. ET. 176 Injured; "We Will Go To Ends Of The Earth" To Catch Those Responsible:

At a news briefing now underway, Boston Police Chief Ed Davis just updated the number of people injured. He says there were "176 casualties that presented at hospitals."

FBI Special Agent in Charge Rick DesLauriers then tells reporters that "we will go to the ends of the earth" to apprehend those responsible.

Update at 10:02 a.m. ET. No Comment On Anyone Being In Custody:

Asked if any suspects are in custody, FBI Special Agent in Charge Rick DesLauriers tells reporters he's "not going to say who might or might not be in custody right now."

Update at 10 a.m. ET. "Act Of Cowardice":

The bombings were an "act of cowardice," Suffolk County (Mass.) District Attorney Dan Conley just told reporters. He promised that "justice will be served."

Update at 9:50 a.m. ET. No Known Additional Threats:

There are "no known additional threats," FBI Special Agent in Charge Rick DesLauriers just told reporters in Boston. He also said the investigation will take some time and asked for the public to continue calling in tips and providing photos or videos taken at the scene.

Update at 9:45 a.m. ET. No Additional Bombs Found:

Authorities are now briefing reporters. Massachusetts Gov. Deval Patrick (D) just said that "all ... parcels have been examined" and no additional bombs were discovered at the scene. He said it should be emphasized that "two and only two explosive devices" were involved in the attack.

Update at 9:10 a.m. ET. BBs May Have Been Packed In Bombs:

"Investigators refused to give any specifics on the bombs and say, for example, where they might have been hidden or whether they were packed with shrapnel for maximum carnage, as is often the case in terror bombings overseas," The Associated Press writes. "But Dr. Stephen Epstein of the emergency medicine department at Beth Israel Deaconess Medical Center said he saw an X-ray of one victim's leg that had 'what appears to be small, uniform, round objects throughout it — similar in the appearance to BBs.' He said it remained to be determined what exactly the objects were."

Update at 8:50 a.m. ET. "Active And Fluid" Investigation:

The Boston Globe writes that "officials last night called the investigation 'very active and fluid.' Authorities were talking to at least one person at Brigham and Women's Hospital, according to sources familiar with the questioning."

Update at 7:45 a.m. ET. On The Young Victim:

"A beloved Dorchester family watching the Boston Marathon near the finish line in Copley Square was caught in one of two bomb blasts that exploded on Monday afternoon," the Dorchester Reporter writes. "Martin Richard, 8, was killed in the explosion, while his sister Jane, 7, suffered a grievous injury to her leg. Their mom, Denise, was also badly hurt in the blast and underwent emergency surgery yesterday to save her life."

Update at 6:50 a.m. ET. More On The Search Of An Apartment In Revere:

As we reported earlier, authorities served a search warrant on a home in the Boston suburb of Revere late Monday, and investigators left with some bags. On its Facebook page, the Revere Fire Department reports that:

    "Deputy Chief, Engine 5, Ladder 1, Cataldo Paramedics & Chief were called in for Operational standby for State Police Bomb Techs for search of a 'person of interest' apartment at 364 Ocean Ave. FBI, ATF, ICE, Boston PD, Revere PD as well as MSP detectives and Bomb Techs from Boston PD and State."

Update at 6:40 a.m. ET. Authorities Seeking Photos.

"Good police work," Tweets the New York Times' Nicholas Kristof, who is in Boston. "At Boston airport, official is asking every person in security line if they have photos from scene."

6:25 a.m. ET. FBI Takes Charge; Estimate Of Number Injured Rises:

On the morning after explosions ripped through an area packed with runners, spectators, race officials, medical personnel and others at the finish line of the Boston Marathon, the FBI is heading up the investigation into who was responsible.

The Associated Press reports that the FBI "has served a search warrant on a home in suburban Boston in the investigation into the Boston Marathon bombing attack. Massachusetts State Police confirm that a search warrant related to the investigation was served Monday night in Revere, but they haven't said anything else. Some investigators were seen leaving the house early this morning, carrying brown paper bags, plastic trash bags and a duffel bag."