US police on Friday captured an ethnic Chechen teenager suspected of staging the Boston marathon bombings, after a massive manhunt that virtually shut down the city and its suburbs.
After a tip from a local resident, police found Dzhokhar Tsarnaev, 19, hiding in a boat in a suburban backyard in Watertown, wounded and weary after a gun battle with police overnight in which his accomplice brother was killed.
"Captured!!! The hunt is over. The search is done. The terror is over. And justice has won. Suspect in custody," Boston police department said on Twitter after Tsarnaev was taken away to applause from relieved residents.
Hundreds of people later descended into the streets of Boston to celebrate, chanting: "USA! USA!"
A neighbor alerted police after finding Tsarnaev "covered with blood" in a boat where he had taken refuge, Boston police chief Ed Davis told reporters.
The University of Massachusetts student was surrounded by a small army of police for a final showdown which lasted nearly two hours. Attempts to negotiate with him failed as he was "not communicating," Davis said.
Following his capture, the suspect was taken to hospital, where he was in serious condition.
"We will determine what happened. We will investigate any associations that these terrorists may have had. And we'll continue to do whatever we have to do to keep our people safe," President Barack Obama said after the capture.
The arrest ended a dramatic four days after two bombs exploded at the Boston Marathon finish line, killing three people and wounding about 180 in the worst attack on the United States since the September 11, 2001 atrocities.
Dzhokhar Tsarnaev and his 26-year-old brother Tamerlan were named as the main suspects. They were also at the center of a violent spree in which one policeman was killed and a second officer wounded.
The bombings traumatized the city with investigators at first seeming to be struggling to find the attackers.
A major breakthrough came when the Federal Bureau of Investigation (FBI) on Thursday released video and picture images of the Tsarnaev brothers as they walked in Boston's Boylston Street where the attacks took place.
Within hours of that press conference, the brothers embarked on a final rampage through the Boston suburbs.
The brothers were captured on a video surveillance camera in a convenience store near the Massachusetts Institute of Technology in Cambridge late Thursday. A police officer was killed in a "vicious assassination" minutes later, Davis said.
The suspects then carjacked a Mercedes, sparking a high-speed police chase to Watertown. Police said the two men hurled explosives out of the car window before the elder brother was shot. Tamerlan Tsarnaev died of bullet wounds and injuries from explosives strapped to his body, a hospital doctor said.
A police officer was wounded in the clash and Tamerlan's use of explosives sparked the fears that his brother also had bombs on his body.
Police launched a huge manhunt on Friday with 9,000 police surrounding Watertown and parts of nearby districts hoping to isolate the teenager who was believed wounded in the shootout in which his brother was killed.
"We assumed that those injuries occurred the evening before. There was an exchange of gunfire at the boat. I don't know if he was struck," Davis said.
Authorities halted all public transport and ordered schools and universities closed and told people in most of the Boston region to stay in their homes.
Tsarnaev was spotted a few minutes after police chiefs and political leaders ended a press conference at which they said they believed the teenager had eluded their operation.
The brothers are ethnic Chechen Muslims who moved to the United States about a decade ago. Their social media pages appeared to express sympathy with the struggle of Chechnya, which has been ravaged by two wars since 1994 between Russia and increasingly Islamist-leaning separatist rebels.
The suspects' father Anzor Tsarnaev told Russia's Interfax news agency his sons had been "set up by the secret services because they are practicing Muslims." But an uncle, Ruslan Tsarni said the pair had put "shame on the entire Chechen ethnicity".
The attack on the marathon sent a hail of nails and shrapnel into crowds of thousands on Boston's Boylston Street.
Boston has held emotional tributes to the dead -- eight-year-old Martin Richard, Boston University graduate student Lu Lingzi of China and Krystle Campbell, a restaurant manager.
More than 100 of the wounded have left Boston hospitals and fewer than 10 of those still in hospital remain in critical condition. Some have horrific injuries and will require new operations, doctors said.
The FBI acknowledged on Friday that an unnamed foreign government had asked about Tamerlan Tsarnaev in 2001 but they had found no key information.