The biggest question in Boston remains: Who did it?

Runner John Ounao crying when he finds friends after several explosions rocked the finish of the Boston Marathon in Boston, Massachusetts, on April 15, 2013. Credit: Getty Images
Runner John Ounao crying when he finds friends after several explosions rocked the finish of the Boston Marathon in Boston, Massachusetts, on April 15, 2013. Credit: Getty Images

Investigators said that two bombs that tore through the crowd at the Boston Marathon finish line Monday may have been fashioned out of shrapnel-filled pressure cookers that were transported in black nylon backpacks.

Boston doctors treating the wounded told reporters today that several of the victims were maimed by what appeared to be pieces of plastic and metal. The fragments were removed during surgery, and turned over to authorities.

Federal Bureau of Investigation Special Agent Richard DesLauriers, who is heading up the investigation, said the pressure cooker bombs may have also contained ball bearings and nails.

As of this evening, no one had taken responsibility for the bombings, and investigators had made no arrests in connection with the attack, which killed three people and injured more than 170. The explosions happened around 2:50 p.m. Monday near the finish line of the Boston Marathon, on Boylston Street.

Authorities said they had received more than 2,000 tips as of noon, many of which were reviewed by 5 p.m.

“The investigation in its infancy. We will thoroughly review each and every piece of evidence,” DesLaurier said, also pleading with the public to provide more information.

The FBI is looking for people who might have seen or heard suspicious activity, including someone carrying a dark, heavy bag near the site of the blasts before the explosions. DesLaurier asked people to inform investigators if they heard any noises similar to an explosion in the days before the attack, as they may indicate a practice blast, and also if anyone overheard discussions a possible attack on the Boston Marathon.

“The range of suspects and motives remains wide open. We’re asking for tips from anyone who may target the event,” he said.

Forensic experts are reconstructing the suspected explosive devices at an FBI lab in Virginia to determine its components. More information is expected during a media briefing this afternoon, but in the meantime DesLaurier asked the public to “remain alert.”

Boston Mayor Thomas M. Menino joined officials at the briefing this evening, commending civilians and emergency respondents for their assistance.

“We are Boston. We are one community and we will not let terror take us over,” he said.

Follow Morgan Rousseau on Twitter: @MetroMorgan
Follow Metro Boston on Twitter: @MetroBOS



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