WASHINGTON (CBSDC/AP) — As investigators try to piece together who was behind the deadly Boston Marathon bombings, al Qaeda is “struggling” to identify who it might be.

CBS News reports that the terrorist group is trying to figure out if the person or persons responsible for the bombing are part of al Qaeda.

“If you read the jihadist blogs that are going on, the ones that have the most credible connections to terrorists groups, they are struggling with the same analysis,” CBS News senior correspondent John Miller said. “They’re saying, ‘We think this was us. We want it to be us.’”

The pressure cooker bombs planted near the Boston Marathon finish line exploded 10 seconds apart, killing three people and injuring 170 others.

Al Qaeda has used these types of pressure-cooker bombs, even recently publishing instructions on how to make them on its online magazine “Inspire.” One of the three devices used in the May 2010 Times Square attempted bombing was a pressure cooker. But because the group doesn’t have enough information about the bombing and are unable to determine if they can claim responsibility.

“This could be the maturation of ideology where we’ve put that call out for the lone wolves to step up and they’ve done it and they just don’t know how to claim responsibility,” Miller said. “It’s interesting to see the investigators are struggling with that question at the same time al Qaeda on the other side of the world is wondering ‘was that us?’”

Authorities have recovered a piece of circuit board that they believe was part of one of the explosive devices, and also found the lid of a pressure cooker that apparently was catapulted onto the roof of a nearby building, an official said Wednesday.

A law enforcement official briefed on the investigation confirmed to The Associated Press that authorities have recovered what they believe are some of the pieces of the explosive devices. The official spoke on condition of anonymity because this person was not authorized to publicly discuss evidence in the ongoing investigation.

A person close to the investigation previously told AP the bombs consisted of explosives put in 1.6-gallon pressure cookers, one with shards of metal and ball bearings, the other with nails.

Also Wednesday, a doctor at Boston Medical Center said two patients, including a 5-year-old child, remain in critical condition there. Dozens of others have been released from hospitals around Boston.

Law enforcement agencies pleaded Tuesday for the public to come forward with photos, videos or any information that might help them solve the twin bombings. Investigators circulated information about the bombs, which involved kitchen pressure cookers packed with explosives, nails and other lethal shrapnel — but the FBI said nobody had claimed responsibility.

“Someone knows who did this,” Richard DesLauriers, FBI agent in charge in Boston, said at a news conference where he detailed the type of clues a bomber might have left. “Importantly, the person who did this is someone’s friend, neighbor, co-worker or relative.”

President Barack Obama branded the attack an act of terrorism but said officials don’t know “whether it was planned and executed by a terrorist organization, foreign or domestic, or was the act of a malevolent individual.” Obama plans to attend an interfaith service Thursday in the victims’ honor in Boston.

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