The investigation of the Boston Marathon bombing is focusing on a suspect or suspects believed to have carried heavy bags or backpacks, but there have still been no arrests or word on who was responsible.
Investigators appeared to have gathered enough evidence at the crime scene yesterday to slightly narrow their search, but it was also not known whether the perpetrators were domestic or foreign, U.S. officials said.
The twin bombs in Boston, which killed three people and injured 176 others, were the worst attack in the United States since security was stepped up across the country after the Sept. 11, 2001 hijacked plane strikes.
A stretch of Boston's Boylston Street almost a mile long and blocks around it remained closed today as investigators searched for clues. The explosions sprayed shrapnel far enough that police were collecting fragments from rooftops along the marathon's course.
Hundreds of people yesterday night turned out at Boston Common, where runners a day earlier had boarded buses to the take them to the race's start line, singing songs including "God Bless America."
Boston Medical Center may be sending home some of the seriously injured people.
"Things are moving along as expected and the patients are doing well," Dr. Peter Burke, the chief of trauma surgery at the hospital told reporters on Wednesday. The hospital initially took in 23 patients, four of whom were released yesterday morning.
Hospitals are saving the shrapnel pieces doctors pick out of the wounded for police. Burke said the fragments include metal, plastic, wood and concrete.
"We've taken on large quantities of pieces we send them to the pathologists and they are available to the police," he said.
NYLON FRAGMENTS, BALL BEARINGS AND NAILS
Among the items recovered at the bomb scene were pieces of black nylon that could be from a backpack, fragments of ball bearings and nails, and possibly the remains of a pressure cooker device, Richard DesLauriers, the Federal Bureau of Investigation's special agent in charge in Boston, told a news conference. Evidence collected at the scene was being reconstructed at the FBI laboratory in Quantico, Virginia, DesLauriers said.
Bomb scene pictures produced by the Boston Joint Terrorism Task Force and released yesterday show the remains of an explosive device including twisted pieces of a metal container, wires, a battery and what appears to be a small circuit board.
One picture shows a few inches of charred wire attached to a small box, and another depicts a half-inch (1.3 cm) nail and a zipper head stained with blood. Another shows a Tenergy-brand battery attached to black and red wires through a broken plastic cap. Several photos show a twisted metal lid with bolts.
A U.S. government official, who declined to be identified, made the pictures available to Reuters.
STUDENT ANGUISH
Residents of the city, which has a large community of students at its many universities, struggled to make sense of the twin bombs that went off at one of Boston's most heavily attended public events, maiming bystanders.
President Barack Obama, who will travel to Boston on Thursday for a memorial service, has called the bombings an "act of terror."
Three people were killed by the blasts.
The youngest to die was an 8-year-old boy, Martin Richard, from the city's Dorchester neighborhood.
Officials identified a second person killed as Krystle Campbell, 29, of Medford, Massachusetts.
"I can't believe this is happening," her mother, Patty, told reporters. "She was the best, you couldn't ask for a better daughter."
The third person who died was a Chinese citizen whose identity was not being made public at the request of the victim's family, the Chinese Consulate in New York said. The victim was a graduate student at Boston University, the university said.
One of the last things the Chinese victim did was post a picture captioned "My wonderful breakfast" on a popular microblog.
The victim's family first realized what might have happened from a posting on a Chinese microblog by the victim's roommate, Hong Kong's Phoenix TV said on its website on Wednesday.
"Everyone, please help me find my roommate", pleaded the post, according to Phoenix. After going to the marathon, "she hasn't come home and ... everyone is very worried."