BOSTON - Federal and local investigative agencies continued to search for clues to explain the deadly Boston Marathon bombings yesterday, and people were encouraged to send in photos and videos.
At least three were killed with more than 144 injured. The explosions tore off limbs and left the streets splattered with blood.
Included in the investigation was a police search overnight of an apartment in Revere, about six miles northeast of here, at the residence of a person whose connection to the bombings was under investigation.
The bombs were placed in pressure cookers, which in turn were placed in backpacks. They were packed with BBs, ball bearings and nails, something done when the bomb maker intends to do maximum damage, inflicting extensive personal injury in a crowded area.
Law enforcement officials said the two bombs were made to look like discarded property and described them as "low explosive," but with "anti-personnel" packing. This fits with statements by doctors who said they had pulled "shrapnel" from the arms and legs of victims.
The bombing yesterday was the worst on U.S. soil since security was tightened after the attacks on Sept. 11, 2001. President Obama said the bombings would be treated as "an act of terror" and that those responsible would "feel the full weight of justice."
Dozens of police and National Guard vehicles are parked around the cordoned-off Boylston Street area in Boston where the bombs went off just before 3 p.m. yesterday.
White House officials said it was too early to say whether the Boston attacks were carried out by a homegrown or foreign group, or to identify a motive.
The Pakistani Taliban, which has threatened attacks in the United States because of its support for the Pakistani government, denied any role in the bombings.
Roupen Bastajian, a state trooper from Smithfield, R.I., had just finished the race when he heard the explosions. "I started running toward the blast," he told the Huffington Post. "And there were people all over the floor. We started grabbing tourniquets and started tying legs. A lot of people amputated. At least 25 to 30 people have at least one leg missing, or two legs missing."
At Massachusetts General Hospital, Alasdair Conn, chief of the emergency room, said, "This is something I've never seen in my 25 years here.... This amount of carnage in the civilian population. This is what we expect from war."
An 8-year-old boy was among the dead, the Boston Globe reported. A 2-year-old was being treated at Boston's Children's Hospital for a head wound, the hospital said.
The blasts put police on alert in major cities across the United States, including Washington, New York and Chicago.
The Boston marathon, which began in 1897, had some 27,000 participants yesterday with 500,000 spectators.
There is a marathon scheduled for London, England next Sunday which authorities there say they now are reviewing due to security concerns. The same is true for a marathon scheduled next Sunday in Madrid.
AFL-CIO President Richard Trumka said, "The country mourns again and struggles to understand acts of indiscriminate and horrifying violence...Such tragedies remind us of the fragility of life, but also of the ability of our communities to come together and heal.
"We commend all the first responders who time and again risk their lives and run towards chaos to attend to the injured and those in need."
Firefighters, members of Boston's International Fire Fighters Association, Local 718, responded right after the two explosions in Copley Square. "We are thankful for our members and the brave first responders helping those in need," said IAFF president, Harold Schaitberger.
Across the U.S., from Washington to Los Angeles, police ramped up security, monitoring landmarks, government buildings, transit hubs and sporting events.
Gov. Deval Patrick said, contrary to earlier reports, no unexploded bombs were found. He said the only explosives found were the ones that went off.
Photo: First responders work outside the medical tent in the aftermath of two blasts that exploded near the finish line of the Boston Marathon on Monday afternoon. The Associated Press