UPDATED 6:15 AM 4/16/13
(BOSTON) -- Hundreds of U.S. law enforcement agents are racing to gather and analyze every shred of evidence from Monday's deadly Boston Marathon bombing for a hint of the attacker.
But the morning after three were killed and nearly 150 more injured in twin explosions, no one has been taken into custody.
Overnight, a tip about possible explosives led federal agents to search an apartment on the fifth floor of a building in the Boston suburb of Revere. Agents later told residents there was nothing to worry about, but the quick and overwhelming law enforcement response underscored the urgency of the FBI's effort to track and stop the people responsible.
"This cowardly act will not be taken in stride," Boston Police Commissioner Ed Davis said. "We will turn [over] every rock to find the people responsible for this."
FBI agents also went to a local hospital to question a 20-year-old Saudi college student who was injured in the blast, but authorities stressed that he is not considered a suspect.
Experts said the most important clues could come from several videos from the race that caught the blasts in real time as well as the explosions themselves.
Authorities said the white smoke seen shortly after one of the detonations indicates small bombs with a simple, low-velocity, explosive mixture -- not military grade.
"[The attackers] may not have the resources as we have seen in other bomb attacks, but they knew how to make the bomb go BOOM," said Nick Casale, a security expert and former New York Police Department officer.
Experts also pointed to large pieces of metal, seen flying through the air in one of the videos, which suggests the bomb may have been concealed in a mail box or trash barrel. The limited damage to nearby buildings tells experts the bomb may have failed to fully function as designed.
If it did somehow malfunction, former NYPD bomb squad member Kevin Barry said Boston was potentially saved from "much more catastrophic injury and possibly more death."
On Tuesday, dozens are recovering in Boston hospitals -- 17 in critical condition -- hours after President Obama told the nation, "Make no mistake, we will get to the bottom of this and we will find out who did this."
"Any individuals, any responsible groups will feel the full weight of justice," Obama said.
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Updated: 6:00pm 4/15/13
Authorities say bombs that exploded near the finish line of the Boston Marathon have killed 3 people and injured more than 130.
Hospitals report that they are treating at least 134 people. Of those, at least 15 are in critical condition.
The injuries ranged from cuts and bruises to amputations. Many victims suffered lower leg injuries and shrapnel wounds. Some suffered ruptured eardrums.
Dr. Richard Wolfe, chief of the department of emergency medicine at Beth Israel Deaconess Medical Center, says one or two of the hospital's 21 patients faced a "high probability of mortality."
Updated: April 15 @ 3:36pm
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Local law enforcement is evaluating the situation in Boston and its implications for Los Angeles. The Los Angeles County Sheriff’s Department has increased security at key locations. Sheriff’s spokesman Steve Whitmore.
The department is working closely with other public safety agencies, although county officials say the Los Angeles County Emergency Operations Center has not yet been activated. Meantime, while the LAPD it has no information at this time that would indicate the events in Boston might have any connection to the Los Angeles area, it is taking precautions. LAPD’s Lt. Andy Neiman.
As far as tonight’s Dodgers game is concerned, a Dodgers spokesman tells KABC News that the team does not comment on security, but that security is paramount for the Los Angeles Dodgers. But the LAPD’s Neiman says will be increasing the security in and around tonight’s Dodger game. The Dodgers take on the San Diego Padres at 7.
Airport Police have increased presence at LAX, Ontario International and Van Nuys airports by deploying bomb-detection canines, additional patrol officers and security personnel, according to Los Angeles World Airports. Officials at the Port of Los Angeles were also under a heightened state of alert. “At this point, we don't believe there is a threat to any of the San Pedro bay port complex, but we have enhanced our security profile,” port spokesman Phillip Sanfield said, “We are watching things closely.”
Security has been stepped up at Metro facilities, including Union Station, with additional officers and K-9 units, according to Marc Littman, a Metro spokesman. In Orange County, Sheriff Sandra Hutchens said deputies would “have an increased presence at local sporting/entertainment venues and other large gathering places.” She also said the department was working with event organizers to review safety protocols, “as well as ensuring our first responders are properly equipped with necessary resources should a similar incident occur.” Sheriff’s spokesman Steve Whitmore adding that these are only precautions.
Acting governor Gavin Newsom said, “There’s no indication of any threats to California or our local communities at this time. However, these events are a reminder to remain vigilant and always report anything unusual to your local law enforcement agency."
Mayor Antonio Villaraigosa issued a statement mid afternoon saying — quote — “Our thoughts and prayers are with the people in Boston in the aftermath of this senseless tragedy. We are working closely with our law enforcement partners to monitor the situation and stand ready to aid Boston in any way possible. The LAPD and other public safety agencies will remain vigilant at all public and sporting events in Los Angeles.”
KABC News Room
BOSTON (KABC) -- Two bombs exploded near the finish line at the Boston Marathon on Monday, killing two people and injuring 23 others. Bomb squads are sweeping the area, checking suspicious packages and are testing for chemicals to help determine what kind of device was used.
The first explosion was heard on the north side of Boylston Street at Marathon Sports running store at 2:50 p.m. ET. It was unclear if the explosion was inside or outside, but it blew out windows in four buildings, officials said. Then about 10 seconds later, another explosion could be heard about 50 to 100 yards away.
An official told ABC News that the explosions were caused by small portable devices.
There was a third explosion at John F. Kennedy Library, but investigators were not yet sure if the incidents were related. The extent of the damage there was not clear, and police say there were no injuries that they know of at JFK Library.
Boston Police Commissioner Edward Davis urged people to stay home and avoided crowded areas while they conduct their investigation.
When the explosions went off, thousands of people fled from the area, and many left bags and personal items at the scene. Davis said each of these items were being treated as suspicious devices.
All victims have been removed from the scene. At least eight of the wounded were in critical condition, according to hospital officials. Several people were shuttled out of the area on wheelchairs, some of them with blood on their faces.
A plume of smoke was seen after the explosions and had a sulfur smell, witnesses said.
"There are a lot of people down," said one man, whose bib No. 17528 identified him as Frank Deruyter of North Carolina.
It was not yet clear who was behind the attack. President Barack Obama has been notified about the explosions and has directed his administration to provide whatever assistance is necessary in the investigation and response.
Shortly after the blasts, police in major cities worldwide increased their security. In Los Angeles, there are increased patrols for transit and other critical areas like the Dodger Stadium, according to sheriff's spokesman Steve Whitmore. The Federal Aviation Administration has also barred low-flying aircraft from within 3.5 miles of the site.
There were over 24,000 participants who streamed across the starting line in Hopkinton on Monday morning for the 117th edition of the Boston Marathon.
ABC News and The Associated Press contributed to this report.
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