President Barack Obama is due to visit Boston
in the next few hours to attend a memorial service for victims of the Boston Marathon bombing.
Two
bombs were detonated near the finish line on Monday, killing three people and
injuring more than 170.
The
president will address an interfaith service as the search for suspects continues.
Investigators
say they have found images of a potential suspect from surveillance camera
footage.
Boston
City Council President Stephen Murphy said a man was seen dropping off a bag at
the scene on Monday.
The
FBI has denied earlier widespread reports that a suspect had been arrested.
Mr
Murphy said detectives had spotted the potential suspect in surveillance
footage from a nearby department store, the Associated Press news agency
reported.
He
said he did not know whether investigators had identified the man, but added:
"They may be on the verge of arresting someone and that's good."
Investigators
have been sifting through thousands of pieces of evidence, ranging from video
recorded on mobile phones to fragments of shrapnel removed from the victims.
Officials
said a circuit board and battery pack - parts of a triggering mechanism - had
been recovered and the lid of a pressure cooker, apparently blown off during
the explosion, was found on the roof of a nearby building.
The
bombs are believed to have consisted of explosives placed in 1.6-gallon
(6-litre) pressure cookers, one with shards of metal and ball bearings, the
other with nails.
Nobody
has claimed responsibility for the bombs, which a source said had been placed
in black bags and left on the ground.
The
twin blasts killed Martin Richard, aged eight, Krystle Campbell, 29, and Lu
Lingzi, a postgraduate student from China.
Shards and shrapnel
Dozens
remain in hospital following the bombs, many of them seriously injured.
A number of victims have had limbs amputated.
"We have a lot of lower extremity
injuries, so I think the damage was low to the ground," Dr Burke said.
"The patients who do have head injuries
were blown into things or were hit by fragments that went up."
At least 58 of the injured have been released
from various hospitals around the city, according to AP.
Of those that remain, a five-year-old child, a
nine-year-old girl and 10-year-old boy were among 17 victims listed as in a
critical condition.
The first explosion went off close to the
finish line at about 14:50 local time (18:50 GMT) on Monday.
Seconds later, as rescuers were rushing to
help the injured, another explosion went off nearby.
The London Marathon - the next major international marathon - is to
go ahead on Sunday.
Organizers have said they will hold a 30-second silence at the start as
a mark of respect.Courtesy: BBC