BOSTON (CBSNewYork/AP) -- Authorities pinpointed a possible suspect Wednesday in the Boston Marathon bombings, and they said surveillance video could provide a critical clue in catching the attacker.
As CBS 2's Jessica Schneider reported, authorities have identified a suspect on a surveillance video they hope will be their break in the case.
Meanwhile, a new image just out Wednesday night appears to show a bag, possibly containing some kind of explosive device, behind a fence at the second explosion site.
CBS News' Bob Orr reported the suspect was seen in a video taken before the blasts. The person is described as a white male and was wearing a white baseball hat, gray hoodie and a black jacket, CBS News reported.
Investigators have been collecting photos and videos from surveillance cameras and other digital media since the twin bombings Monday that killed three people and wounded more than 170 others.
Orr said a person was seen on surveillance video carrying a black backpack and talking on a cellphone moments before the blast at the site of what became the second explosion on Monday.
According to CBS sources, investigators zeroed in on the suspect using cellphone records that showed who was making calls in the area at that exact time.
"According to my sources, the man can be seen placing the backpack on the ground and he is on a cellphone call at the time," Orr said. "While he's on the phone, I'm told, an explosion takes place at the finish line of the race course. As soon as that blast went off, this man then, according to my sources, can be seen leaving that area and kind of just mingling in the crowd."
Authorities continued to ask members of the public for help and for any photos or videos that may provide any additional leads.
Meanwhile on Wednesday afternoon, the Moakley Federal Courthouse in Boston was evacuated due to a bomb threat. WCBS 880's Alex Silverman spoke with people who heard over a loudspeaker "code red, evacuate."
"It came over the loudspeaker 'code red.' We've all had training what to do...Get out of the building, go to your meeting spot, so we did that," court employee Jessica Lewis told CBS 2's Schneider.
Hundreds of journalists were pushed back 100 yards while courthouse workers rushed out.
REPORTS OF PERSON IN CUSTODY DEEMED INCORRECT
There were reports earlier in the day, attributed to a law enforcement official speaking to the Associated Press, that a suspect was in custody in connection with the bombings. However, the FBI and the U.S. Attorney's office in Boston said that no arrests had been made.
An official news briefing, originally scheduled for 5 p.m. and later for 8 p.m., was postponed.
"Contrary to widespread reporting, there have been no arrests made in connection with the Boston Marathon attack,'' the FBI said in a statement. "Over the past day and a half, there have been a number of press reports based on information from unofficial sources that has been inaccurate. Since these stories often have unintended consequences, we ask the media, particularly at this early stage of the investigation, to exercise caution and attempt to verify information through appropriate official channels before reporting.''
The Boston Police Department also sent a tweet denying the reports:
The official who spoke to the AP did so on condition of anonymity and stood by the information even after it was disputed. The official, who was not authorized to divulge details of the investigation, had said the suspect was expected in federal court in Boston.
CBS News correspondent John Miller explained that authorities need to be careful in revealing information about the case.
"This is a tortured decision inside any investigation. The calculus is -- do we want to keep this lead to a small group of investigators and try to go grab them, or do we want to go public?" Miller said. "The risks run on both sides. On one hand, if you're looking for him and you don't catch him, the further away he might get. The flip side is, if he doesn't know you know who he is, or that you're looking for him, he may stay in place. When you go public with that, he may run."
AUTHORITIES DETAIL PRESSURE COOKER BOMB
Authorities have also recovered the lid of a pressure cooker that apparently was catapulted onto the roof of a nearby building, and a piece of circuit board that they believe was part of one of the explosive devices, a law enforcement source confirmed to CBS News on Wednesday.
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.
An intelligence bulletin issued to law enforcement and obtained by the Associated Press and the Reuters news agency late Tuesday included pictures of a mangled pressure cooker, a torn black bag, a circuit board and a battery connected to wires, all of which the bulletin said were from the two bombs used in the attack.
Pressure cooker bombs can help boost the power of relatively small devices by briefly constraining the blast. And when the cookers do explode, they can add large chunks of metal to the shrapnel spray.
"Placed carefully, such devices provide little or no indication of an impending attack," the report said.
Investigators said they have not yet determined what was used to set off the explosives.
Similar pressure-cooker explosives have been used in Afghanistan, India, Nepal and Pakistan, according to a July 2010 intelligence report by the FBI and Homeland Security. Also, one of the three devices used in the May 2010 Times Square attempted bombing was a pressure cooker, the report said.
No one has claimed responsibility for the Boston attack. Al Qaeda recently published instructions on how to make such bombs on its online magazine "Inspire" and CBS News reports the terrorist group is trying to figure out if the person or persons responsible for the bombing are part of al Qaeda.
Bomb and counterterrorism expert Frank Skinner said the execution of the attack suggests a level of sophistication and planning.
"It was a methodical, detailed effort by somebody to create a lot of carnage and death," Skinner said. "They didn't just show up and place bombs. I think they maybe watched it for a year or two before they made their attack."
Experts said because the explosive devices were planted near ground level, the force of the blast was directed low and out towards the street, causing the massive leg injuries. Most of the victims suffered lacerations and penetration injuries from the shrapnel and metal objects placed in the bomb.
Expert: Attack Suggests Level Of Sophistication
DOCTORS SAY VICTIMS SUSTAINED WAR-LIKE INJURIES
Scores of victims of the Boston bombing remained in hospitals, many with grievous injuries. Doctors compared the unusual injuries to war injuries caused by land mines and improvised explosive devices.
"Almost all of them had such severe trauma in their lower extremity that was beyond salvation," said Dr. George Velmahos with Massachusetts General. "So, I would consider them almost automatic amputees. We just completed what the bomb had done."
Doctors say once released from hospitals, most of the victims face a long rehabilitation process.
The blasts killed 8-year-old Martin Richard, of Boston, and 29-year-old Krystle Campbell, of Medford. The Shenyang Evening News, a state-run Chinese newspaper, identified the third victim as Lu Lingzi. She was a graduate student at Boston University.
President Barack Obama will be in Boston Thursday for an interfaith service for the marathon bombing victims.
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