Webcam vision of Boston Marathon finish line after explosions

Boston bombs pressure cookers filled with ball bearings

AMERCIA will go "to the ends of the earth" to hunt down those responsible for the bombings at the Boston Marathon, the special FBI agent in charge of the investigation vowed today, as it emerged that the two bombs were made from pressure cookers filled with ball bearings - designed to cause maximum damage.

Through the day the toll of injured rose, from 140 in the morning to 176 by afternoon.

Of the three fatalities the youngest was eight-year-old Martin Richard, whose mother and sister were among the 17 victims still in a critical condition last night. Restaurant manager Krystle Campbell, 29, was later confirmed as the second person killed.

AP reported that doctors also said they removed a host of sharp objects from the victims, including nails that were sticking out of one little girl's body.

"We've removed BBs and we've removed nails from kids. One of the sickest things for me was just to see nails sticking out of a little girl's body," said Dr David Mooney, director of the trauma center at Boston Children's Hospital.

Two children remain in critical condition at the hospital with serious leg injuries. Mooney said that tourniquets applied by emergency responders at the race saved the children's lives.

Doctors at Massachusetts General Hospital also say they removed metal fragments from victims of the two bombs.

Yet as more harrowing details of victims emerged, officials gave no indication that they had anyone in custody or had made any solid headway on the case.

During the early hours of yesterday morning police with a search warrant entered a high-rise flat in Revere, a suburb five miles from the scene of the blasts, and were later seen leaving with a large brown bag.

Mourning the loss of her daughter Krystle to the attack at the Boston Marathon, Patty Campbell said 'you couldn't ask for a better daughter,' adding, 'this doesn't make any sense.'

Police said the occupier offered them a "lead" on their investigation, but was not a suspect.

By morning any timidity about calling the incident a terror attack had melted away, including on the part of the President himself.

"This was a heinous and cowardly act, and given what we now know about what took place, the FBI is investigating it as an act of terrorism," he said in a brief White House appearance.

"Any time that bombs are used to target innocent civilians it is an act of terror."

But he, in common with other officials and experts, conceded that with no claim of responsibility made and the investigation still in its earliest phases, many pieces of the puzzle remained missing.

"What we don't yet know … is who carried out this attack or why, whether it was planned and executed by a terrorist organisation - foreign or domestic - or [whether it] was the act of a malevolent individual."

"This will be a worldwide investigation," FBI special agent Richard DesLauriers told reporters at a mid-morning press conference in Boston.

"We will go to the ends of the earth to identify the subject or subjects who are responsible for this despicable crime and we will do everything we can to bring them to justice." Mr DesLauriers said his agents had received "voluminous tips" since the attack.

Officials said only two devices in the end were found and both had gone off.

One source said to be close to the investigation told reporters that the bombs were made from pressure cookers packed with ball-bearings, a statement consistent with hospital reports of victims suffering from shrapnel injuries.

They had apparently been placed in rucksacks and left on the ground.

A large section of central Boston remained a crime scene yesterday, with block after block around Copley Square in the city's picturesque 19th-century Back Bay neighbourhood cordoned off with metal barriers and swarming with local, state and federal agents.

Harry Flores, a local man in his forties who has been watching runners complete the final mile of the marathons since he was a boy, was walking away from the finish line when the first bomb went off behind him.

"It was scary. People started screaming and crying," he said.

"It was still scary this morning. It still feels tense around here - look at the police, the machine guns. I was scared to get on the train.

"They searched my bags and there [were] police everywhere. But I had to [take the train] because I work near here. I was scared something else was going to happen."

Mr Flores was standing at the corner of Boylston Street and Arlington Street, about three blocks down from the finishing line, when the bombs went off. Yesterday at that corner a policeman was standing guard in front of a barrier blocking the way to the blast site.

Arlington had been swept clean overnight but behind the officer, on Boylston, stretched a sea of debris from the marathon preserved for investigators: empty water bottles, flyers, plastic bags, torn flags, discarded newspapers.

Officials could be seen coming in and out of a white tent in the distance.

Across the road from the cordon, the pavement running along the Public Garden was loaded with a bank of cameras and reporters - and scores of local and state police officers, some carrying arms.

Backing them up were members of the Massachusetts National Guard in their military fatigues, an incongruous sight on a sunny, New England spring morning.

Tighter security in place for London Marathon

While there was nothing to indicate a continuing or specific threat in the wake of the attacks either in Boston or elsewhere, tighter security precautions were being rushed into place across America and indeed globally, including in Britain, which hosts the London Marathon this weekend, and Russia, which will hold the World Athletics Championships in Moscow in August as well the 2014 Winter Olympics in Sochi.

The Russian Sports Minister Vitaly Mutko described the attack in Boston as "a grave signal".

President Obama yesterday ordered that all American flags on official and military buildings around the world be flown at half mast until this weekend to honour the victims in Boston.

The events in Boston will be seen as a wake-up call to a country that has not seen such public carnage in a public setting associated with terror - aside from attacks by gunmen - since the 9/11 horrors of September 2001.

"No matter how many days, months or years pass without a major terrorist attack, it only takes one such attack to bring us back to the cruel reality," Interpol chief Ron Noble told the Associated Press.

  New York was among cities beefing up protection of its landmarks and deploying mobile anti-terror units as an additional precaution. Mayor Michael Bloomberg said the police department was ready to protect the city.

"Some of the security steps we are taking may be noticeable," he said. "And others will not be."

Organisers of the London Marathon will watch how the investigation unfolds with special attention.

"The attacks mean that we will be assessing our security protocols," a British security official who spoke on condition of anonymity told the Associated Press. 

"There is some initial information coming out … but it is too early to draw any conclusions. There doesn't appear at this point, however, to be a wider threat."

Surgeons at different hospitals in the Boston area all told a story of awful injuries, including patients who have undergone amputations.

"This is something I've never seen in my 25 years here … this amount of carnage in the civilian population," said Alasdair Conn, chief of emergency services at Massachusetts Hospital.  "This is what we expect from war."

Officials repeatedly called on the public to hand in any photographs or videos from the scene saying they might contain important information even if it is not obvious at first glance.

"There has to be thousands of photographs and videos. I would encourage you to bring forward anything, you might not think it's significant but it might be of value to this investigation," said Sate Police Colonel Timothy Alben.

The Police Commissioner of Boston, Ed Davis, was pressed on whether enough had been done ahead of the race to protect runners. He revealed the areas where the bombs went off had twice been swept, the second time just an hour before the winners crossed the line.

He said he was now confronting "the most complex crime scene we have dealt with in the history of our department".

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