Armed guards protected the hospital where the wounded surviving Boston Marathon bombing suspect was in serious condition today and unable to be questioned to determine the motives behind the worst terrorist attack in the US since September 11, 2001.



US officials said a special interrogation team for high-value suspects was waiting to question 19-year-old Dzhokhar Tsarnaev, whose older brother and alleged accomplice was killed Friday morning in a wild shootout in suburban Boston.



Authorities planned to invoke a rare public safety exception to enable the team to interrogate Tsarnaev without first advising him of his right to remain silent to avoid self-incrimination and be provided an attorney, a warning typically given to criminal suspects .



The FBI's website says the exception "permits law enforcement to engage in a limited and focused unwarned interrogation" of a suspect and introduce any statements gathered as evidence in a criminal prosecution. The FBI says "police officers confronting situations that create a danger to themselves or others may ask questions designed to neutralize the threat without first providing a warning of rights."



The capture of Dzhokhar Tsarnaev lifted days of anxiety for Boston and Americans everywhere, but little was known about the motivation of the ethnic Chechen brothers.



President Barack Obama vowed investigators would solve that mystery. "The families of those killed so senselessly deserve answers," said Obama, who branded the suspects "terrorists." Obama said the capture closed "an important chapter in this tragedy," but he said there are many unanswered questions about the Boston bombings, including whether the two men had help from others.



"When a tragedy like this happens, with public safety at risk and the stakes so high, it's important that we do this right," he said. "That's why we take care not to rush to judgment - not about the motivations of these individuals, certainly not about entire groups of people."



Yesterday, less than an hour after authorities said the search for the 19-year-old college student had proved fruitless and lifted a daylong order that had kept Boston-area residents in their homes, a man emerged from his Watertown home and noticed blood on the pleasure boat parked in his backyard. He lifted the tarp and found the wounded Tsarnaev, known the world over as Suspect No. 2.



Soon after that, the 24-hour drama that had shut down a metropolitan area of millions while legions of police went house to house looking for the remaining suspected Boston Marathon bomber was over.



Boston police announced via Twitter that Tsarnaev was in custody. They later wrote: "CAPTURED!!! The hunt is over. The search is done. The terror is over. And justice has won. Suspect in custody."

ENDGAME

Tamerlan Tsarnaev, 26, died in the shootout early in the day (local time). At one point, he was run over by his younger brother in a car as he lay wounded, according to investigators.

1 of 26 The Massachusetts State Police released this image taken from a police helicopter as police surrounded the marathon bombing suspect. 2 of 26 The Massachusetts State Police released this image taken from a police helicopter as police surrounded the marathon bombing suspect. 3 of 26 Twitter This photo is allegedly of the suspect Dzhokhar Tsarnaev laying face up on the ground after his capture. International media are working on verifying the image. 4 of 26 Law enforcement officials depart the search area in Watertown for Dzhokar Tsarnaev after the stay at home alert has been lifted. 5 of 26 Residents are asked to leave their home as SWAT teams conduct a house to house search for Dzhokar Tsarnaev, the one remaining suspect in the Boston Marathon bombing. 6 of 26 A girl looks out her window as law enforcement searches for Dzhokar Tsarnaev, the remaining suspect in the Boston Marathon bombings, in Watertown, Massachusetts. 7 of 26 A photo from the profile of Dzhokhar Tsarnaev taken from social networking site VK. 8 of 26 Anzor Tsarnaev, who calls himself father of Dzhokhar and Tamerlan Tsarnaev, the two suspects in the Boston Marathon bombings, gives an interview in Makhachkala in which he claims his sons have been framed. 9 of 26 MIT Patrol Officer Sean A. Collier, 26, of Somerville, Massachusetts is pictured in this undated MIT handout photo. Collier was shot April 18, 2013 on the MIT campus following an altercation with the suspects in the Boston Marathon bombing, according to media reports. He was transported to Massachusetts General Hospital, where he was pronounced dead. 10 of 26 Massachusetts Bay Transportation Authority (MBTA) police officer Richard Donohue Jr., is shown in this handout photo provide by the MBTA April 19, 2013. Donahue was injured in a shootout late April 18, 2013 with Boston Marathon bombing suspects Tamerlan and Dzhokhar Tsarnaev. 11 of 26 Reuters A member of the SWAT team trains a gun on an apartment building during a search for the remaining suspect in the Boston Marathon bombings. 12 of 26 Reuters SWAT teams enter a suburban neighborhood to search for the remaining suspect in the Boston Marathon bombings in Watertown. 13 of 26 Reuters A bomb technician walks away after preparing the controlled detonation of a suspicious object during a search for a suspect in the Boston Marathon bombing. 14 of 26 Reuters SWAT teams enter a suburban neighborhood to search for the remaining suspect in the Boston Marathon bombings in Watertown. 15 of 26 Reuters Members of the SWAT team cover an apartment during the search for the remaining suspect in the Boston Marathon bombings. 16 of 26 Reuters SWAT teams enter a suburban neighborhood to search for the remaining suspect in the Boston Marathon bombings in Watertown. 17 of 26 Boston Poilice NEW IMAGE: Police have released this new photo showing the man believed to be a suspect in the Boston Marathon bombing, taken at a 7-Eleven store in Cambridge, just across the river from Boston. 18 of 26 Reuters Superintendent and Colonel of the Massachusetts State Police Timothy Alben speaks to reporters about the status of the two suspects in the Boston Marathon bombings in Watertown. 19 of 26 Reuters A law enforcement vehicle carries a bomb disposal device through Watertown. 20 of 26 Reuters Law enforcement officials during a search for the two men suspected of setting off two explosions during the Boston Marathon. 21 of 26 Suspects wanted for questioning in relation to the Boston Marathon bombing. 22 of 26 Suspects wanted for questioning in relation to the Boston Marathon bombing. 23 of 26 Reuters Police officers keep a man on the ground in Watertown, Massachusetts. 24 of 26 Reuters Law enforcement officers talk at the scene of a police manhunt in Watertown, Massachusetts. 25 of 26 Reuters Police officers keep a man on the ground in Watertown, Massachusetts. 26 of 26 Reuters Heavy armed police officers arrive at the scene of a manhunt in Watertown, Massachusetts.

- Timeline of events

The bloody endgame came four days after the bombing and just a day after the FBI released surveillance-camera images of two young men suspected of planting the pressure-cooker explosives that ripped through the crowd at the marathon finish line, killing three people and wounding more than 180.



The two men were identified by authorities and relatives as ethnic Chechens from southern Russia who had been in the US for about a decade and were believed to be living in Cambridge, Massachusetts. But investigators gave no details on the motive for the bombing.



Obama said the capture closed "an important chapter in this tragedy", but he said there are many unanswered questions about the Boston bombings, including whether the two men had help from others. He urged people not to rush judgment about their motivations.



"When a tragedy like this happens, with public safety at risk and the stakes so high, it's important that we do this right," he said. "That's why we take care not to rush to judgment - not about the motivations of these individuals, certainly not about entire groups of people."



The breakthrough came when a man in Watertown saw blood on a boat parked in a yard and pulled back the tarp to see a man covered in blood, authorities said. The resident called authorities and when police arrived, they tried to talk the suspect into getting out of the boat, said Boston Police Commissioner Ed Davis.



"He was not communicative," Davis said.



Instead, he said, there was an exchange of gunfire - the final volley of one of the biggest manhunts in American history.



Watertown residents who had been told in the morning to stay inside behind locked doors poured out of their homes and lined the streets to cheer police vehicles as they rolled away from the scene.



Celebratory bells rang from a church tower. Teenagers waved American flags. Drivers honked. Every time an emergency vehicle went by, people cheered loudly.



Police said three other people were taken into custody for questioning at an off-campus housing complex at the University of the Massachusetts at Dartmouth where the younger man may have lived.



"Tonight, our family applauds the entire law enforcement community for a job well done, and trust that our justice system will now do its job," said the family of 8-year-old Martin Richard, who died in the bombing.



Also killed in the attack was a Chinese student.



Chechnya has been the scene of two wars between Russian forces and separatists since 1994, in which tens of thousands were killed in heavy Russian bombing. That spawned an Islamic insurgency that has carried out deadly bombings in Russia and the region, although not in the West.



The older brother had strong political views about the United States, said Albrecht Ammon, 18, a downstairs-apartment neighbour in Cambridge. Ammon quoted Tsarnaev as saying that the US uses the Bible as "an excuse for invading other countries".



The FBI interviewed the older brother at the request of a foreign government in 2011, and nothing derogatory was found, according to a federal law enforcement official who was not authorised to discuss the case publicly and spoke on condition of anonymity.



The official did not identify the foreign country or say why it made the request.



The FBI was swamped with tips after the release of the surveillance-camera photos - 300,000 per minute - but what role those played in the capture was unclear. State Police spokesman Dave Procopio said police realised they were dealing with the bombing suspects based on what the two men told a carjacking victim during their long night of crime.



The search for the younger brother all but paralysed the Boston area for much of the day. Officials shut down all mass transit, including Amtrak trains to New York, advised businesses not to open, and warned close to 1 million people in the entire city and some of its suburbs to stay inside and unlock their doors only for uniformed police.



About midday (local time), the suspects' uncle Ruslan Tsarni, of Maryland, pleaded on television: "Dzhokhar, if you are alive, turn yourself in and ask for forgiveness."



The brothers had built an arsenal of pipe bombs, grenades and improvised explosive devices and used some of the weapons in trying to make their getaway, said Rep. Dutch Ruppersberger, a member of the House of Representatives Intelligence Committee.



Tamerlan Tsarnaev had studied accounting as a part-time student at Bunker Hill Community College in Boston for three semesters from 2006 to 2008, the school said.



Dzhokhar Tsarnaev was registered as a student at the University of Massachusetts Dartmouth. Students said he was on campus this week after the Boston Marathon bombing. The campus closed down yesterday along with colleges around the Boston area.

FATHER STANDS BY 'ANGEL' SON

The father of the suspects, Anzor Tsaraev, said his younger son was a second-year student studying medicine.



"My son is a true angel ...," he said by telephone from the Russian city of Makhachkala. "He is such an intelligent boy. We expected him to come on holidays here."



He added, "They were set up, they were set up! I saw it on television; they killed my older son Tamerlan."

He ended the call angrily, saying, "Leave me alone, my son's been killed."

SCHOLARSHIP TO 'LOSER' NEPHEW

The city of Cambridge announced two years ago that it had awarded a US$2500 scholarship to him. At the time, he was a senior at Cambridge Rindge & Latin School, a highly regarded public school whose alumni include Matt Damon, Ben Affleck and basketball Hall of Famer Patrick Ewing.



Tsarni, the men's uncle, said the brothers travelled to the US together from Russia. He called his nephews "losers" and said they had struggled to settle in the US and ended up "thereby just hating everyone".



Shortly before Dzhokhar Tsarnaev's capture, the White House said Obama had spoken by phone with Russian President Vladimir Putin about the investigation.



The White House said in a statement that Obama "praised the close co-operation that the United States has received from Russia on counter-terrorism, including in the wake of the Boston attack".

SUSPECT PORTRAITS



Tamerlan practised martial arts and boxing, even aspiring to fight on the US Olympic team. Dzhokhar had been on the wrestling team at a prestigious school and won a scholarship from his city to pursue higher education.

Tamerlan had studied accounting as a part-time student at Bunker Hill Community College in Boston for three semesters from 2006 to 2008, the school said. Dzhokhar was registered as a student at the University of Massachusetts Dartmouth.

Neighbours recalled the ethnic Chechen brothers, living on a quiet street in Cambridge, Massachusetts, riding bikes and skateboards.



Tamerlan was once arrested for domestic assault on a girlfriend.



"I don't have a single American friend. I don't understand them," he was quoted as saying in a photo package that appeared in a Boston University student magazine in 2010.



He identified himself as a Muslim and said he did not drink or smoke: "God said no alcohol." He said he hoped to fight for the US Olympic team and become a naturalised American. He said he was studying at Bunker Hill Community College to become an engineer.



Dzhokhar attended the prestigious Cambridge Rindge and Latin school, participating on the wrestling team. In May 2011, his senior year, he was awarded a $2500 scholarship from the city to pursue higher education, according to a news release at the time. That scholarship was celebrated with a reception at city hall.

Government officials said Tamerlan traveled to Russia last year and returned to the US six months later. The officials spoke on condition of anonymity because they couldn't publicly talk about an investigation in progress. One said Tsarnaev traveled out of John F. Kennedy International Airport in New York.



Dzhokhar's page on the Russian social networking site Vkontakte said that before moving to the United States he attended School No. 1 in Makhachkala, the capital of Dagestan, a predominantly Muslim republic in Russia's North Caucasus that has become an epicenter of the Islamic insurgency that spilled over from the region of Chechnya.



On the site, he describes himself as speaking Chechen as well as English and Russian. His world view is described as "Islam" and he says his personal goal is "career and money."



Tim Kelleher, a wrestling coach for a Boston school that competed in 2010 against Dzhokhar's team, said the young man was a good wrestler and that he'd never heard him express any political opinions.



"He was a tough, solid kid, just quiet," Kelleher said.



Before moving to Dagestan, the Tsarnaev family lived in Kyrgyzstan, a former Soviet republic in Central Asia. Leila Alieva, who went to school with Tamerlan Tsarnaev in the Kyrgyz town of Tokmok, remembers an educated family.



"Tamerlan was in the same year, but in a different class," Alieva said. "He was a very positive boy, a good student, a jock, a boxer. He used to win all the (boxing) competitions in town.



She remembered Dzhokhar as a little boy and said the family also had two sisters. She described the family as "very educated, of middle income". They had relatives in the US and left, she said.



"I can't believe they were involved in the explosions, because Tamerlan was a very positive guy, and they were not very Islamist," Alieva said. "They were Muslim but had a secular lifestyle."

- AP with Reuters