Investigators Work To Pinpoint Those Responsible for Boston Marathon Bombings

The day after two bombs exploded near the finish line of the Boston Marathon, killing three and injuring at least 176 to date, government officials and investigators revealed a preliminary theory about the nature of the explosives used and the way in which they may have been transported.

Richard DesLauriers, the FBI agent in charge of the investigation, said that it appeared that kitchen-type “pressure-cookers” were probably the devices used in the attack, and that they probably had been modified to release various types of shrapnel upon explosion. Investigators found pieces of shrapnel, in the form of “fragments of BB’s and nails”, in the blast zone.

In addition to the shrapnel, DesLauriers devoted particular attention to a few shreds of fabric recovered near the finish area.

“Among items partially recovered are pieces of black nylon which could be from a backpack,” DesLauriers said, adding that investigators concluded Tuesday morning that “both of the explosives were placed in a dark-colored nylon bag or backpack. The bag would have been heavy due to the components believed to be in it.”

Though he cautioned that the evidence has not yet been examined by the FBI’s lab in Quantico, VA., DesLauriers asked civilians to try and recall if they had seen somebody carrying “an usually heavy, dark-colored bag around the time of the blast and in the vicinity of the blast.”

While DesLauriers said that the FBI had received over 2,000 tips by noon on Tuesday, he admitted that “the range of suspects and motives remains wide open.”

Boston area officials also fielded questions about the preparedness of the Boston Police Department.

Boston Police Commissioner Edward F. Davis said that his department had identified the finish area as a risk zone before the race, and had developed a security plan to account for that.

“There were more officers assigned to this race than we had ever assigned before,” he said. “We were particularly concerned with the finish line this year and assigned more officers down in that area. I think if you look at the videotapes you can see that.”

He also pointed to the difficulties of securing such a public event.

“[The marathon] is a soft target,” Davis said. “When you have an event like this, you can’t lock it down like a military operation. It needs to be open to the public.”

Davis also said that the finish area had been swept for explosives on two occasions—both hours before the explosions—Monday morning by an explosive ordinance disposal unit. Neither he nor DesLauriers would comment on whether the explosives used might have been undetectable by bomb-sniffing dogs.

Throughout Tuesday, law enforcement officials that stressed that the public may hold the key to the investigation. “We are hoping that if there is any video or graphic evidence that you will please contact the FBI hotline or the city’s hotline,” said Gene Marquez, an agent with the Bureau of Alcohol, Tobacco, Firearms, and Explosives.

“You might not think it’s significant, but it might have some value to this investigation,” concurred Col. Timothy Alben of the Massachusetts State Police.

The developments in the FBI-led investigation into the bombings came after an unusual day in Back Bay. Much of the neighborhood remained off-limits to the public, causing delays for public transportation and forcing drivers to take alternative routes.

Reporters crowded the accessible areas near the crime scene. One restaurant on Newbury Street—Stephanie’s on Newbury—attracted a multitude of cameramen straining to capture photographs of a patio of dirty tables with plates full of half-consumed meals, untouched since Monday afternoon, when restaurant patrons and staffers fled the bombs.

Even the streets that weren’t barricaded—and which would usually be busy during the Tuesday morning commute—were largely deserted, with the exception of the media. Scores of television relay trucks clustered around Boston Common, and also congregated on Commonwealth Avenue between Dartmouth and Exeter Streets.

By Tuesday evening, the names of two of the three victims who have died so far as a result of the explosions had been released. Martin Richard, 8, from Dorchester was watching his father, William Richard, finish the race when the bombs blew; his sister and mother are still recovering from serious injuries, though his brother was unharmed in the blast. Krystle Campbell, 29, a former Harvard employee and relative of two Harvard University staff members, was described by family members as a loyal fan of the marathon.

The third victim has not yet been identified, though she is believed to have been a Chinese national.

Another media briefing is scheduled for Wednesday afternoon. President Barack Obama will visit Boston on Thursday morning and will attend an interfaith service at the Cathedral of the Holy Cross.

—Staff writer Matthew Q. Clarida can be reached at clarida@college.harvard.edu. Follow him on Twitter @MattClarida.

This article has been revised to reflect the following correction:

CORRECTION: April 17, 2013

An earlier version of this article incorrectly stated the location of the restaurant Stephanie’s on Newbury. In fact, the restaurant is on Newbury Street, not Commonwealth Avenue.