WATERTOWN, Mass. — The two suspects in the Boston Marathon bombing killed an MIT police officer and hurled explosives at police in a car chase and gun battle overnight that left one of them dead and his brother on the run, authorities said Friday as thousands of officers swarmed the streets in a manhunt that all but paralyzed the Boston area.

The suspects were identified by law enforcement officials and family members as Dzhokhar and Tamerlan Tsarnaev, ethnic Chechen brothers from Dagestan, which neighbors Chechnya in southern Russia. They lived near Boston and had been in the U.S. for about a decade, an uncle said.

Tamerlan Tsarnaev, a 26-year-old who had been known to the FBI as Suspect No. 1 and was seen in surveillance footage in a black baseball cap, was killed overnight, officials said. His brother, a 19-year-old college student who was dubbed Suspect No. 2 and was seen wearing a white, backward baseball cap in the images from Monday’s deadly bombing at the marathon finish line — escaped.

Their uncle in Maryland, Ruslan Tsarni, pleaded on live television: “Dzhokhar, if you are alive, turn yourself in and ask for forgiveness.”

Authorities in Boston suspended all mass transit and warned close to 1 million people in the entire city and some of its suburbs to stay indoors as the hunt for Suspect No. 2 went on. Businesses were asked not to open. People waiting at bus and subway stops were told to go home.

From Watertown to Cambridge, police SWAT teams, sharpshooters and FBI agents with armored vehicles surrounded various buildings as police helicopters buzzed overhead.

“We believe this man to be a terrorist,” said Boston Police Commissioner Ed Davis. “We believe this to be a man who’s come here to kill people.”

In Cambridge, Bryce Acosta, 24, came out of his home with his hands up.

“I had like 30 FBI guys come storm my house with assault rifles,” he said. They yelled, “Is anybody in there?” and began searching his house and an adjacent shed, leaving after about 10 minutes.

Authorities gave no details on how Dzhokhar Tsarnaev escaped.

Authorities in Connecticut searched an Amtrak train and a commuter rail train for Dzhokhar Tsarnaev but didn’t find anything.

The bombings on Monday killed three people and wounded more than 180 others, tearing off limbs in a spray of shrapnel and instantly raising the specter of another terrorist attack on U.S. soil.

Chechnya was the scene of two wars between Russian forces and separatists since 1994 and the conflict spawned an Islamic insurgency that engulfed the region.

Authorities have shed no light on the motive for the Boston bombing and have said it is unclear whether it was the work of domestic or international terrorists or someone else entirely with an unknown agenda.

The endgame — at least for Suspect No. 1 — came just hours after the FBI released photos and video of the two young men at the finish line and appealed to the public for help in identifying and capturing them. Tips came pouring in to the FBI immediately, but exactly how authorities managed to close in on the two was not immediately disclosed.

Tsarni, the men’s uncle, told The Associated Press that the brothers traveled here together from Russia. He called his nephews “losers” and said they had struggled to settle themselves in the U.S. and ended up “thereby just hating everyone.”

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, the school said. The campus closed down along with colleges around the Boston area.

Their father, Anzor Tsarnaev, said in a telephone interview with The Associated Press from the Russian city of Makhachkala that his younger son, Dzhokhar, is “a true angel.”

He said his son was studying medicine. “He is such an intelligent boy. We expected him to come on holidays here,” the father said.

The city of Cambridge announced two years ago that it had awarded a $2,500 scholarship to Dzhokar Tsarnaev, who was listed as a senior at Cambridge Rindge & Latin School, a highly regarded public school whose alumni include Matt Damon, Ben Affleck and NBA star Patrick Ewing.

The images released by the FBI depict the two young men walking one behind the other near the marathon’s finish line. Richard DesLauriers, FBI agent in charge in Boston, said Suspect No. 2 in the white hat was seen setting down a bag at the site of the second of two deadly explosions.

Authorities said surveillance tape recorded late Thursday showed Suspect No. 2 during a robbery of a convenience store in Cambridge, near the campus of MIT, where a university police officer — 26-year-old Sean Collier — was shot to death while responding to a report of a disturbance.

From there, authorities said, the two men carjacked a man in a Mercedes-Benz, keeping him with them in the car for half an hour before releasing him at a gas station in Cambridge. The man was not injured.

Massachusetts State Police spokesman Dave Procopio said police figured out the carjackers were the marathon bombing suspects in part because of what they said to the carjacking victim. Procopio did not elaborate.

The search for the vehicle led to a chase that ended in Watertown, where authorities said the suspects threw explosive devices from the car and exchanged gunfire with police. A transit police officer was severely wounded, authorities said.

Doctors at a Boston hospital where Tamerlan Tsarnaev died said they treated a man with a possible blast injury and multiple gunshot wounds.

Watertown resident Kayla Dipaolo, 25, was waiting for a bus that was to evacuate her and others from their neighborhood.

She said she was woken up overnight by gunfire and a large explosion that sounded “like it was right next to my head … and shook the whole house.” She was looking at the front door when a bullet came through the side paneling. SWAT team officers were running all over her yard, she said.

“It was very scary,” she said. “There are two bullet holes in the side of my house and by the front door there is another.”

Christine Yajko said she heard two loud explosions and gunfire. She said a police officer later knocked on her door and told her there was an undetonated improvised explosive device in the street and warned her to stay away from the windows.

“It was on the street, right near our kitchen window,” she said.

The brothers also started out the night in a Honda CRV and used it to carjack the SUV. The CRV was later found abandoned in the morning in Boston.

In the past, insurgents from Chechnya and neighboring restive provinces in the Caucasus have been involved in terror attacks in Moscow and other places in Russia.

Those raids included one in Moscow in 2002 in which a group of Chechen militants took 800 people hostage and held them for two days before special forces stormed the building, killing all 41 captors. Also killed were 129 hostages, mostly from the effects of the gas Russian forces used to subdue the attackers.

Chechen insurgents also launched a 2004 hostage-taking raid in the southern Russian town of Beslan, where they took hundreds of hostages. The siege ended in a bloodbath two days later, with more than 330 people, about half of them children, killed.

Insurgents from Chechnya and other regions also have launched a long series of bombings in Moscow and other cities in Russia.