BOSTON: A suspect in the deadly Boston Marathon bombings was taken into custody in a breakthrough that came less than 48 hours after the attack, a law enforcement official briefed on the investigation said yesterday.

The official spoke shortly after several media outlets reported that a suspect had been identified from surveillance video taken at a Lord & Taylor department store between the sites of the blasts, which killed three and wounded more than 170. The dead included a child, a young woman and a female student from China.

The official was not authorized to divulge details of the investigation and spoke to The Associated Press on condition of anonymity. The suspect was expected at a Boston courthouse, the official said.

Richard DesLauriers, FBI agent in charge in Boston, said at a news conference that the “range of suspects and motives remains wide open.” He vowed to “go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime.”

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 (6-ltr) 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, Virginia, for analysis.

The FBI said it is looking at what Boston television station WHDH said are photos sent by a viewer that show the scene right before and after the bombs went off. The photo shows something next to a mailbox that appears to be a bag, but it's unclear what the significance is.

“We’re taking a look at hundreds of photos and that's one of them,” said Jason Pack, FBI spokesman in Boston.

Investigators said they have not yet determined what was used to set off the explosives. Pressure-cooker explosives have been used in international terrorism, and have been recommended for lone-wolf operatives by Al-Qaeda’s branch in Yemen.

But information on how to make the bombs is readily found online, and US officials said Americans should not rush to judgment in linking the attack to overseas terrorists. DesLauriers said there had been no claim of responsibility for the attack.

Obama plans to visit Boston today to to attend an interfaith service in honor of the victims. He has traveled four times to cities reeling from mass violence, most recently in December after the schoolhouse shooting in Newtown, Connecticut.

Boston police and firefighter unions announced a $ 50,000 reward for information leading to arrests.