View a related story: Chattanooga officials: Security on track for championship cycling race
BOSTON - Federal agents zeroed in Tuesday on how the Boston Marathon bombing was carried out - with kitchen pressure cookers packed with explosives, nails and other lethal shrapnel - but said they still didn't know who did it and why.
The FBI and other law enforcement agencies repeatedly appealed to the public to come forward with photos, videos or anything suspicious they might have seen or heard.
"The range of suspects and motives remains wide open," Richard DesLauriers, FBI agent in charge in Boston, said at a news conference. He vowed to "go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime."
President Barack Obama branded the attack an act of terrorism but said officials don't know "whether it was planned and executed by a terrorist organization, foreign or domestic, or was the act of a malevolent individual."
Scores of victims of the Boston bombing remained in hospitals, many with grievous injuries, a day after the twin explosions near the marathon's finish line killed three people, wounded more than 170 and reawakened fears of terrorism. A 9-year-old girl and 10-year-old boy were among 17 victims listed in critical condition.
Heightening jitters in Washington, where security already had been tightened after the bombing, a letter addressed to a senator and poisoned with ricin or a similarly toxic substance was intercepted at a mail facility outside the capital, lawmakers said.
There was no immediate indication the episode was related to the Boston attack. Senate Majority Leader Harry Reid said the letter was sent to Republican Sen. Roger Wicker of Mississippi.
Officials found that the bombs in Boston consisted of explosives put in ordinary, 1.6-gallon pressure cookers, one with shards of metal and ball bearings, the other with nails, according to a person close to the investigation who spoke on condition of anonymity because the probe was still going on.
Both bombs were stuffed into black duffel bags and left on the ground, the person said.
DesLauriers confirmed that investigators had found pieces of black nylon from a bag or backpack and fragments of BBs and nails, possibly contained in a pressure cooker. He said the items were sent to the FBI laboratory at Quantico, Va., for analysis.
Investigators said they have not yet determined what was used to set off the Boston explosives.
Pressure-cooker explosives have been used in international terrorism, and have been recommended for lone-wolf operatives by Al-Qaida's branch in Yemen.
But information on how to make the bombs is readily found online, and U.S. officials said Americans should not rush to judgment in linking the attack to overseas terrorists.
DesLauriers said that there had been no claim of responsibility for the attack.
He urged people to come forward with anything suspicious, such as hearing someone express an interest in explosives or a desire to attack the marathon, seeing someone carrying a dark heavy bag at the race, or hearing mysterious explosions recently.
"Someone knows who did this," the FBI agent said.
The bombs exploded 10 or more seconds apart, tearing off victims' limbs and spattering streets with blood, instantly turning the festive race into a hellish scene of confusion, horror and heroics.
The blasts killed 8-year-old Martin Richard of Boston and 29-year-old Krystle Campbell of Medford, Mass.
The Chinese Consulate in New York says a Chinese national is the third person killed in the blasts.
An official at the consulate's press section, who was not authorized to give his name, said that one Chinese student was injured and another died in the blast.
Doctors who treated the wounded corroborated reports that the bombs were packed with shrapnel intended to cause mayhem.
- The Associated Press
The Boston Marathon is a family affair. The 116th annual race began on Monday no differently than in previous years, with families lining the 26.2-mile course.
"My husband and I always went to cheer on the runners," said Kendra Stanton Lee, an assistant professor at Southern Adventist University in Collegedale.
"We would likely have been there with our two children had we still lived in Boston."
In fact, Lee and her family would have likely been at the race cheering next to their former neighbors, the Richards.
Lee, like many people across the nation, is in shock at the bombings and hurting for the families that are experiencing loss. Everyone is thinking, "this could have been us."
The Richard family regularly attended the race and cheered for runners as they neared the finish line at Copley Square. This year Martin Richard stood next to his parents, Denise and Bill, and siblings Henry and Jane, as he had several other times.
The bombs that went off near the finish line took Martin's life and seriously injured Denise and Jane.
Martin, a third-grade student, was the first among three victims of the bombings to be identified. His mother and his younger sister were among scores injured and were still reported to be in the hospital late Tuesday.
"My wife and daughter are both recovering from serious injuries," Bill Richards said in a statement Tuesday afternoon. "We thank our family and friends, those we know and those we have never met, for their thoughts and prayers."
Lee has not spoken with the family yet, but said she is one of many who woke up to this worst possible news.
The Richard family is known for making their neighbors feel at home in Dorchester.
"The family is very dedicated to improving the community," Lee said.
She remembers a day when Denise invited her to join her family on a walk.
"We walked to a local park and Martin was riding his bike ahead of us," Lee said. "Denise kept yelling, "Marrrtin! Stop at the corner!" and Martin always would."
"He was a very precious little boy."