BOSTON (CBSNewYork/AP) -- One of the explosive devices used in the bombings of the Boston Marathon appeared to have been in a metal pressure cooker packed with nails and ball bearings, CBS News reported.
As CBS 2's Lou Young reported, a law enforcement source told CBS News that one of the explosive devices appeared to have been placed in a metal pressure cooker which had been placed in a black nylon bag or backpack.
Investigators also found pieces of an electronic circuit board possibly indicating a timer was used in the detonation of the bomb.
The two bombs that exploded were made to look like discarded property, a law enforcement official told CBS News. It is still unknown if one or both bombs were in garbage cans. One may have been on the sidewalk.
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The bombs were described as "low explosive," but with "anti-personnel" packing. This is consistent with doctors reporting shrapnel pulled from victims. The official said there were apparently things like BBs, ball bearings and nails in the bombs.
While no information has been released about whether the attack was domestic or international in nature, authorities have noted that the pressure cooker design for the bombs is favored by al-Qaeda.
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.
"Placed carefully, such devices provide little or no indication of an impending attack,'' the report said.
But since the other attacks, authorities noted, the design has been widely circulated and could have been picked up by an independent operator – a lone wolf.
The Pakistani Taliban, which claimed responsibility for the 2010 attempt in Times Square, has denied any role in the Boston Marathon attack.
Regardless, Suffolk County, Mass. District Attorney Daniel Conley said someone will pay for Monday's attack.
"Make no mistake an act of cowardice and of this severity cannot be justified or explained. It can only be answered," Conley said.
Meanwhile, police and federal agents appealed to the public Tuesday for amateur video and photos that might yield clues to the bombing as the chief FBI agent in Boston vowed to find whoever carried out the deadly attack.
There has to hundreds if not thousands," said Massachusetts State Police Col. Timothy Alben. "I would urge you to bring everything, even if you think it's not important."
President Barack Obama, who will travel to Boston on Thursday, said the bombings were an act of terrorism, but investigators do not know if they were carried out by an international organization, domestic group or a "malevolent individual.'' He said, "the American people refuse to be terrorized.''
On Capitol Hill, Defense Secretary Chuck Hagel called the bombings "a cruel act of terror'' and said "a thorough investigation will have to determine whether it was planned or carried out by a terror group, foreign or domestic.''
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Boston Police Commissioner Edward Davis said investigators gathered a large number of surveillance video from businesses and intend to go through them frame by frame.
"It's our intention to go through every frame of every video that we have to determine exactly who was in the area," Davis said, calling it the most complex crime scene in history of the department. "Even as we were removing victims yesterday, officers were assigned to go into local establishments and secure those videos."
Davis urged the public to try to get back to normal, but to keep eyes peeled for anything suspicious.
"We want you to live your life. We want you to be vigilant and there's no reason to not come into the city, but we do have a threat and we're working diligently to try and reduce that threat and we want you to go about your business. Give us a little room in Copley Square," Davis said.
"There has to be hundreds, if not thousands, of photos and videos'' that might help investigators, state police Col. Timothy Alben said.
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Massachusetts Gov. Deval Patrick said contrary to earlier reports, no unexploded bombs were found. He said the only explosives were the ones that went off.
"Two and only two explosive devices were found yesterday," Patrick said. "All other parcels in the area of the blasts have been examined but there are no unexploded bombs -- there were no unexploded explosive devices found."
"I think that happened as a result of some suspect packages that were disrupted. But we only have two devices that we're aware of and both those devices were involved in the damage in the explosive incident," ATF Special Agent In Charge Gene Marquez said.
Special Agent in Charge Richard DesLauriers said there are no known additional threats and agents are following a number of leads.
"We will go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime, and we will do everything we can to bring them to justice,'' said DesLauriers.
Overnight, authorities descended on an apartment complex in Revere, about a 20-minute drive from downtown Boston, where the FBI served a search warrant, WBZ-TV reported.
Massachusetts State Police confirmed that a search warrant related to the investigation into the explosions was served Monday night in Revere, but provided no further details.
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Some investigators were seen leaving the Revere house early Tuesday carrying brown paper bags, plastic trash bags and a duffel bag.
Earlier, CBS News senior correspondent John Miller said authorities were questioning a Saudi national, who was under guard at an area hospital.
He was seen running from the explosion, and a civilian chased him down and tackled him. He was turned over to Boston police and was interviewed by the FBI.
Local and federal agents are now saying the man is not a suspect in the marathon bombings.
CBS News has confirmed that the Revere apartment officials raided Monday night is the home of a spectator and not a suspect. One of the men who lives at the residence told reporters, including CBS 2's Young, that the man who was being looked at got hurt by the bomb and had nothing to do with the blasts. The Saudi man originally mentioned, related to the investigation, is not a suspect.
"Bottom line – this is going to take some time," the man's roommate said.
The fiery explosions took place about 10 seconds and about 100 yards apart, knocking spectators and at least one runner off their feet, shattering windows and sending dense plumes of smoke rising over the street and through the fluttering national flags lining the route.
Blood stained the pavement, and huge shards were missing from window panes as high as three stories. Victims suffered broken bones, shrapnel wounds and ruptured eardrums.
Davis said there were 176 casualties at hospitals, at least 17 of whom were critically injured. At least eight children were being treated at hospitals.
Three people were killed in the attack. So far, two of the victims have been identified. The third victim has been identified as a Boston University graduate student whose name is being withheld by the university until family notification.
That victim was also a Chinese national, and a woman, according to the Consulate General of the People's Republic of China. The consulate also declined to identify the victim.
Martin Richard, 8, was watching Monday's race and had gone to get ice cream before returning to the area near the finish line before the blasts.
On Tuesday, authorities identified the second victim as 29-year-old Krystle Campbell of Arlington, CBS 2 has learned.
William Campbell said his daughter was "very caring, very loving person, and was daddy's little girl" and that the loss has devastated the family, the Associated Press reported.
Campbell's mother, Patty Campbell, spoke to reporters on Tuesday afternoon, and expressed her distress and devastation.
"We are heartbroken at the death of our daughter...she was a wonderful person," Patty Campbell said. "Everybody that knew her, loved her."
The victim's mother added "You couldn't ask for a better daughter...I can't believe this has happened. This doesn't make any sense."
A growing memorial for the victims of the attack was set up Tuesday night, CBS 2 reported.
The Boston Marathon is one of the world's oldest and most prestigious races and about 23,000 runners participated. The race honored the victims of the Newtown, Conn., shooting with a special mile marker in Monday's race.
Boston Athletic Association president Joanne Flaminio previously said there was "special significance'' to the fact that the race is 26.2 miles long and 26 people died at Sandy Hook Elementary School.
The bombings occurred about four hours into the race and two hours after the men's winner crossed the finish line. By that point, more than 17,000 of the athletes had finished the marathon, but thousands more were still running.
Spectator Cherie Falgoust was waiting for her husband, who was running the race.
"I was expecting my husband any minute," she said. "I don't know what this building is ... it just blew. Just a big bomb, a loud boom, and then glass everywhere. Something hit my head. I don't know what it was. I just ducked."
Across the U.S. and around the globe, police have tightened security, monitoring landmarks, government buildings, transit hubs and sporting events.
In New York City, police have stepped up security at city landmarks, hotels, subway stations, transit facilities and other prominent landmarks.
Bloomberg said Tuesday the measures will stay in place until authorities know more about what happened in Boston.
(TM and © Copyright 2013 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2013 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)
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