A suspect in the Boston Marathon bombings was on the run Friday as thousands of law enforcement authorities cast a wide net that virtually shut down the Massachusetts capital amid warnings the man was possibly armed with explosives.
Authorities say Dzhokar Tsarnaev escaped an overnight shootout in suburban Watertown with police that left his brother Tamerlan Tsarnaev -- the other man wanted in the bombings -- dead.
"Investigators are recovering a significant amount of homemade explosives" from the scene of the shootout, Massachusetts State Police spokesman David Procopio told CNN.
It was not immediately clear what explosives were recovered, but the discovery followed a violent night in which authorities say the brothers allegedly hurled explosives at pursuers after killing an officer, robbing a convenience store and hijacking a car.
Tamerlan Tsarnaev was wearing explosives and a triggering device when he died, a source briefed on the investigation told CNN's Deborah Feyerick on condition of anonymity.
Gov. Deval Patrick called on residents in the city and its suburbs to stay inside "with their doors locked."
After more than 15 hours, police officers in full body armor, carrying automatic weapons had finished about 70% of their massive door-to-door search of the area, Col. Timothy Alben of the Massachusetts State Police said.
Police flooded the area, traveling the streets in convoys and going door-to-door to track the suspect down.
It was unclear how long the manhunt would go on disrupting the lives of the millions in Boston. Already, the Boston Red Sox announced they were postponing Friday night's game against the Kansas City Royals "to support efforts of law enforcement officers." NHL's Boston Bruins also postponed its game against the Pittsburgh Penguins.
Police ordered businesses in the suburb of Watertown and nearby communities to stay closed and told residents to stay inside and answer the door for no one but authorities. Boston authorities advised the same. The city's subway, bus, Amtrak train systems and Greyhound and Bolt Bus -- a regional carrier -- have been shut down. Taxi service across the city also was suspended for time during the manhunt. Every Boston area school is closed.
Boston's public transit authority sent city buses to Watertown to evacuate residents while bomb experts combed the surroundings for possible explosives.
The search followed a violent night in which authorities say the two men allegedly hurled explosives at pursuers after killing Massachusetts Institute of Technology police Officer Sean Collier, robbing a convenience store and hijacking a car.
The violence began late Thursday -- just hours after authorities released photos of the suspects in the marathon bombings -- with the robbery of a convenience store, according to Alben.
Soon after, in Cambridge, across the Charles River from Boston, MIT officer Collier was shot and killed while he sat in his car, the Suffolk County District Attorney's Office said in a statement.
The two suspects, according to authorities, then hijacked a vehicle at gunpoint in Cambridge, telling the driver that they were the marathon bombers, a law enforcement source told CNN's Joe Johns.
At some point, apparently at a gas station, that source said, the driver escaped.
Police, who were tracking the vehicle using its built-in GPS system, picked up the chase in Watertown. The pursuit went into a residential neighborhood, with the suspects throwing explosives at police.
A firefight erupted and ultimately one bomber -- later identified as Tamerlan Tsarnaev -- got out of the car. Police shot him, and his brother ran over him as he drove away, according to the source, who spoke on condition of anonymity.
Richard H. Donohue Jr., 33, a three-year veteran of the transit system police force, was shot and wounded in the incident and taken to a hospital, a transit police spokesman said Friday. The officer's condition was not immediately known.
Details about the suspects
Police believe the brothers are the same men pictured in images released Thursday by the FBI as suspects in the marathon bombing that killed three people and wounded dozens on Monday.
The men are shown in the images walking together near the marathon finish line.
The first suspect -- apparently Tamerlan Tsarnaev, according to authorities -- appears in the images wearing a dark hat, sunglasses and a backpack. The second suspect, wearing a white cap, is the one who remains at large, police said.
According to a source briefed on the investigation, the brothers came from the Russian Caucasus region and had moved to Kazakhstan at a young age before coming to the United States several years ago.
A statement from the office of Chechnya's president echoed that: "According to preliminary information, coming from the relevant agencies, the Tsarnaev family moved many years ago out of Chechnya to another Russian region," press secretary Alvi Kamirov told Russia's semi-official Interfax news agency. "After that they lived for some time in Kazakhstan, and from there went to the U.S. where the family members received a residence permit. Therefore the individuals concerned did not live as adults in Chechnya."
Two sources told CNN that Dzhokar Tsarnaev came to the U.S. as a tourist with his family in the early 2000s and later asked for asylum. He became a naturalized U.S. citizen in 2012. Tamerlan Tsarnaev was not a naturalized citizen, a source said. He came "a few years later" and was lawfully in the United States as a green-card holder.
Tamerlan Tsarnaev had studied at Bunker Hill Community College and wanted to become an engineer, the source said. He then took a year off to train as a boxer.
The source said that a posting on a social media site in the elder brother's name included the comments: "I don't have a single American friend. I don't understand them."
Dzhokar Tsarnaev attended Cambridge Rindge & Latin, a public high school, said Eric Mercado, who graduated a year behind the suspect. Mercado said Tsarnaev had worked at Harvard University as a lifeguard.
"We hung out; we partied; we were good high school friends," Mercado told CNN.
"We're all, like, in shock. We don't really understand. There were no telltale signs of any kind of malicious behavior from Dzhokar. It's all coming as a shock, really."
Mercado said he lived a block away from the suspect and did not know his older brother.
Dzhokar Tsarnaev is currently registered as a student at University of Massachusetts Dartmouth, which ordered its campus evacuated on Friday. The school is located 65 miles south of Cambridge, just west of New Bedford.
Larry Aaronson, Dzhokar Tsarnaev's neighbor and a former teacher at the high school Tsarnaev attended, called him a "wonderful kid."
"He was so grateful to be here, he was compassionate, he was caring, he was jovial," Aaronson told CNN.
CNN's Ben Brumfield, Terence Burke, Dave Alsup, Carma Hassan, Jake Tapper, Drew Griffin, Steve Almasy and Chandler Friedman contributed to this report.