FBI investigating Boston Marathon bombings as "act of terrorism"
A person briefed on the Boston Marathon investigation says the explosives were in 6-liter pressure cookers and placed in black duffel bags.
The person says the explosives were placed on the ground and contained shards of metal, nails and ball bearings. The person spoke on the condition of anonymity because the investigation was ongoing.
The person says law enforcement officials have some of the bomb components but did not yet know what was used to set off the explosives.
President Barack Obama said Tuesday the bombings were an act of terrorism but investigators do not know if they were carried out by an international or domestic organization, or perhaps by a "malevolent individual."
No unexploded devices found
Massachusetts Governor Deval Patrick says no unexploded bombs were found at the Boston Marathon. He says the only explosives were the ones that went off Monday.
Three people were killed, including an 8-year-old boy, and more than 150 injured by two explosions just seconds apart near the finish line Monday.
Authorities are appealing to the public for amateur video and photos that might yield clues to who carried out the bombing.
A 15-block area in Boston's Back Bay remains blocked off as investigators comb the area for clues in Monday's marathon bombing.
At least 17 people are in critical condition following the attack.
No suspects have been identified in the case. Federal authorities are classifying the attack as an act of terrorism.
The National Guard has been called in to provide security around the locked down streets, and have turned the popular Copley Square into a staging area.
The FBI has taken the lead role in the investigation, using its resources in Boston and Washington, DC in the probe.
The ATF is bringing in explosive experts to investigate. Some 30 forensic specialists are en route or on the scene.
Boston's Police commissioner says it's the most complex crime scene his department has ever had to process.
Meantime, Boston Police have increased security throughout the city as Boston's mayor encourages locals to return to work where possible. Boston leaders say the city will remain under tight security until further notice. It will take several days to clear the scene.
Treating the injured
A spokeswoman as Massachusetts General Hospital said Tuesday that doctors there treated "everything from cuts and bruises to amputations."
Dr. Stephen Epstein of the Department of Emergency Medicine at Beth Israel Deaconess Medical Center says in an email the X-ray of a leg he saw has "what appears to be small, uniform round objects throughout it - similar in the appearance to BBs."
He says exactly what the objects are remains to be determined.
An eight-year-old boy is among three people killed in the explosions, Martin Richard of Dorchester, Massachusetts, was at the finish line with his mother and sister waiting for their father Bill Martin to cross. Martin's mother and sister were severely injured in the blast.
"They are beloved by this community. It is surreal. It is tragic," said a Dorchester community leader who knows the family.
A candle burned on the stoop of the family's single-family home in the city's Dorchester neighborhood Tuesday, and the word "Peace" was written in chalk on the front walkway.
Neighbor Betty Delorey says Martin loved to climb the neighborhood trees, and hop the fence outside his home.
The children's father, Bill, is the director of a local community group. The boy's mother, Denise, works at the Neighborhood House Charter School, where her children attend classes.
Restaurant manager, 29, among the dead
A 29-year-old restaurant manager was also killed in the blast.
Her father says Krystle Campbell, of Medford, Mass., had gone with her best friend to take a picture of the friend's boyfriend crossing the finish line on Monday afternoon.
William Campbell says his daughter, who worked at a restaurant in nearby Arlington, was "very caring, very loving person, and was daddy's little girl." He says the loss has devastated the family.
He says the friend was seriously injured in the explosion.
It took only seconds after the blast for witnesses and bystanders to race to the aid of those injured.
One person who offered assistance to the injured was Dr. Alan Panter of Gainesville, Florida. Panter, an emergency room physician, was near the finish line waiting for his wife Teresa to finish her 16th Boston Marathon when the blast happened.
"I was surrounded by a lot of people trying to watch the runners cross the finish line. The people to my left took the blow from the blast. Most of them dropped. People behind me actually did too. And I was just standing there without a scratch," he said. "When I first spun around I saw one lady bleeding from a leg wound. I put some compression on that and realized that all the people that had been to my left had gone down. And I just started helping with the other bystanders. Pulling people actually apart because they were lying in a pile basically with mangled limbs and started working on each person as you could."
"The sidewalk volunteers, instead of running away, they stopped and fell and worked the people. When the Boston Athletic Association volunteers came they came with supplies and once you got to the medical tent it was all that an ER physician ask for. There were cots, IVs, nurses and physicians. It was well prepared," he added.
"It was about an hour or an hour and a half before I was able to get my baggage in the bus and call him because I was grabbing phones where they had held us but we couldn't get any calls out so I didn't know," said his wife, Teresa.
If you are trying to get in touch with a friend or family member in Boston, call 617-635-4500.
If you have a tip related to the investigation, call 1-800-494-TIPS.