Boston Marathon blasts: Investigators eye 'range of suspects and motives'

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FBI / AP

The remains of a pressure cooker that the FBI says was part of one of the bombs that exploded during the Boston Marathon.

By Richard Esposito and Jeff Black, NBC News

Two days after the deadly twin blast at the Boston Marathon, investigators said they were looking at a variety of suspects and motives as they learned more about the makeup of the bombs themselves.

The two bombs appeared to have each contained tiny nails, smaller than the ones used to hang pictures, ?fine nails? or brads, according to one of the people assigned to the case. And the devices themselves appear to have been delivered to the scene in two duffel bags.

Investigators have begun the process of recovering tiny pieces of bombs to learn how they were made. So far, they know the bombs were made from pressure cookers filled with ball bearings and nails ? a method used for decades in terror bombings. But no suspects are in custody and investigators are asking the public for help. NBC's Pete Williams reports.

On Tuesday afternoon, the FBI?s lead investigator, Richard DesLauriers, made a passionate plea for information from the public, saying the ?range of suspects and motives remains wide open? as the probe into who might be responsible for the attacks begins.

?Someone knows who did this,? he said.

?Importantly, the person who did this is someone?s friend, neighbor, coworker or relative. We are asking anyone who may have heard someone speak about the marathon, or the date of April 15, in any way that indicated that he or she may have targeted this event to call us.?

Late Tuesday, the FBI and Homeland Security Department published photos in a law enforcement?bulletin?showing twisted metal that they said were the remains of one of the pressure-cooker bombs used in the attack.

Another image showed a fragment of material from the bag or sack that had held one of the bombs, according to the bulletin.

FBI / AP

A black bag the FBI says contained one of the bombs that exploded during the Boston Marathon.

Sources involved in the investigation said that the pressure-cooker bombs were powerful "homemade claymore,"?directional explosives that appeared to include a triggering mechanism using a battery pack and a circuit board. Both of those elements were recovered at the scene.

"It appeared to be built from scratch but with a sophisticated triggering mechanism. And frankly, at the end of the day, all bombs are crude devices, and it is the way they are triggered that can be sophisticated," said one official with strong knowledge of explosives. "They functioned as designed."

According to a FBI-Department of Homeland Security document, which included the pictures, a preliminary examination of photographs and on-scene reports show that one of the bombs consisted of a pressure cooker with an undetermined main charge. The other device was also housed in a metal container, but so far there is not enough evidence to determine if it was also a pressure cooker, the document stated.

Also Tuesday evening, the Chinese consulate in New York confirmed that the third victim was a Chinese national. The victim, whose family has requested she not be identified, was also a student at Boston University, the school said.?

From the London Marathon to the Kentucky Derby, the security plans that had been in place for big, upcoming public gatherings are being reevaluated in the wake of the Boston bombings that killed three people and injured more than 170. NBC's Tom Costello reports

Identified as among?the dead were 8-year-old Boston boy Martin Richard, who was waiting at the finish, and Krystle Campbell, 29, of the Medford, Mass.

Massachusetts Gov. Deval Patrick also announced that President Barack Obama would attend an interfaith service honoring the victims of the tragedy at 11 a.m. on Thursday at Cathedral of the Holy Cross in South Boston.

Patrick and Boston Mayor Thomas Menino also said a new centralized fund was set up in order to to gather donations to help families affected by the tragedy. Called The One Fund Boston, contributions can be made through a website, onefundboston.org.?

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This story was originally published on Tue Apr 16, 2013 10:50 PM EDT

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