Brian Snyder / Reuters Police officers take position during a search for the Boston Marathon bombing suspects in Watertown, Massachusetts April 19, 2013. Police on Friday killed one suspect in the Boston Marathon bombing during a shootout and mounted a house-to-house search for a second man in the suburb of Watertown after a bloody night of shooting and explosions in the city's streets. REUTERS/Brian Snyder (UNITED STATES - Tags: CRIME LAW) 
 
 Boston and its suburbs, universities and transit system were on total lockdown Friday as police hunted door to door for marathon bombing suspect Dzhokhar Tsarnaev -- on the loose after his accomplice brother was killed in a stunning chain of events that left one cop dead and another injured, officials said. 
 
 During a desperate effort to flee after their photos were released by the FBI, the brothers carjacked a Mercedes SUV and told the driver they were the men behind Monday's double-blast attack at the race and had just killed a campus security officer, a source told NBC News. The driver was released unhurt. 
 
 The older brother, Tamerlan Tsarnaev, was killed after a wild chase and firefight, but Dzhokhar was still at large in a densely populated area, and an associate was being sought. Adding to the nightmare, an explosive was found in Boston Friday morning and disabled, an official said. 
 
 The suspects' uncle, Ruslan Tsarni, called them "losers" and urged Dzhokhar, a naturalized American citizen of Chechen origin, to turn himself in. 
 
 "We're ashamed," he thundered outside his Maryland home. 
 
 Three dozen FBI agents were surrounding the Cambridge, Mass., home where the brothers grew up after moving to the U.S. a decade ago, seeking asylum. They feared it could be booby-trapped and planned to conduct a controlled explosion before a full search, state police said. 
 
 NBC's Lester Holt reports from Watertown, Mass., where Boston and state police, SWAT teams and a helicopter are engaged in a tense search for a suspect in the Boston Marathon bombing who is still at large. 
 
 Across the area, as police cars screamed down streets and helicopters hovered overhead, authorities urged the public to stay inside and keep their doors locked to anyone but law-enforcement officers. 
 
 "There is a massive manhunt under way," Massachusetts Gov. Deval Patrick said. "We are asking people to shelter in place." 
 
 Subways and buses were shut down, and Amtrak service to Boston was cut. Harvard University, Boston University, the Massachusetts Institute of Technology and Emerson University were closed. The University of Massachusetts' Dartmouth campus was being evacuated because someone wanted in the case is registered at the school. 
 
 The lockdown initially affected more than 300,000 people in Cambridge, Watertown, Newton, Brighton, Allston and Belmont, but by 8 a.m., the entire city of Boston was paralyzed, officials said. 
 
 Watertown, where the second suspect was last seen, was the epicenter of a sprawling search. By 12:30 p.m., police estimated, 60 percent of the homes had been searched. Frightened residents were trapped inside as convoys of heavily armed officers and troops arrived by the hour. 
 
 The overnight violence began at MIT about five hours after the FBI released surveillance photos of two "extremely dangerous" men suspected of planting two bombs near the finish line of Monday's Boston Marathon, killing three and wounding 176. 
 
 Read more: Who are the brothers accused of the Boston Marathon bombing? 
 
 Tips about the identity of the suspects were still pouring in when the Tsarnaev brothers fatally shot MIT patrol officer Sean Collier, 26, in his vehicle at 10:20 p.m., law enforcement officials said. 
 
 Uncredited / AP FBI photos of the Boston Marathon bombing suspects, brothers from the Chechen Republic. The man on the left is dead. The man on the right, Dzhokhar Tsarnaev, is still at large. 
 
 The brothers then carjacked a Mercedes SUV, holding the driver captive for a half-hour while they tried to use his cash card to get money from three ATM's, a source said. At the first, they put in the wrong number; at the second, they took out $800 and at the third, they were told they had exceeded the withdrawal limit, the source said. 
 
 The man was released unharmed at a gas station in Cambridge, sources said. As they sped toward Watertown, a police chase ensued and the suspects tossed explosive devices out the window, officials said. 
 
 There was a long exchange of gunfire, according to Andrew Kitzenberg of Watertown, who took photos of the clash from his window and spread them on social media. 
 
 “They were also utilizing bombs, which sounded and looked like grenades, while engaging in the gunfight,” he told NBC News in an interview. “They also had what looked like a pressure-cooker bomb. 
 
 “I saw them light this bomb. They threw it towards the officers,” he said. “There was smoke that covered our entire street.” 
 
 A transit officer, identified as Richard H. Donahue, 33, was seriously injured during the pursuit. Authorities said he was in surgery at Mount Auburn Hospital. 
 
 Kitzenberg said he saw the firefight end when Tamerlan Tsarnaev ran toward the officers and ultimately fell to the ground. 
 
 Tamerlan -- the man in the black hat from FBI photos released six hours earlier -- had an improvised explosive device strapped to his chest, law enforcement officials said. 
 
 Dzhokhar -- who was wearing a white hat in the surveillance photos from the marathon -- drove the SUV through a line of police officers at the end of the street, Kitzenberg said. 
 
 Police said Dzhokhar has a Massachusetts driver's license and lives in Cambridge. He was described as light-skinned and with brown, curly hair, and wearing a gray hoodie. The FBI released more photos of him, including a surveillance camera photo from a 7-Eleven. 
 
 His father, in Russia, told the Associated Press he was "a true angel" and described him as a medical student who was expected to visit for the holidays. 
 
 Authorities painted a starkly different picture. 
 
 "We believe this man to be a terrorist," Boston Police Commissioner Ed Davis said. "We believe this to be a man who's come here to kill people." 
 
 Armored humvees and busloads of law-enforcement could be seen rolling into Watertown in the hours after the gunfight. 
 
 "We've got every asset we could possibly muster on the ground right now," Patrick said. 
 
 Later Friday morning, attorney General Eric Holder and FBI Director Robert Mueller headed to the White House to brief President Obama on the developments. 
 
 Secretary of State John Kerry, who is from Massachusetts, praised law enforcement for their work during "a pretty direct confrontation with evil." 
 
 "In the past few days we have seen the best and we've seen the worst of human behavior, and it's the best that all of us really want to focus on," he said. 
 
 Senate Intelligence Committee chairwoman Dianne Feinstein told NBC News it's clear the marathon bombing was "a terrorist attack." 
 
 "It's also clear, you know, that you know you don't have to be a card-carrying member of any terrorist group to commit a terrorist attack," she said. 
 
 NBC News' Jonathan Dienst and Kasie Hunt contributed to this story 
 
 Slideshow: Search for suspects in Boston Marathon bombings / A tense night of police activity that left a university officer dead on campus just days after the Boston Marathon bombings and amid a hunt for two suspects caused officers to converge on a neighborhood outside Boston, where residents heard gunfire and explosions. Launch slideshow 
 
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 This story was originally published on ||||| Julio Cortez/AP Police secured an area of Watertown during the manhunt. 
 
 In the waning moments of daylight, police descended Friday on a shrouded boat in a Watertown backyard to capture the suspected terrorist who had eluded their enormous dragnet for a tumultuous day, ending a dark week in Boston that ­began with the bombing of the world’s most prestigious road race. 
 
 The arrest of 19-year-old Dzhokhar Tsarnaev of Cambridge ended an unprecedented daylong siege of Greater Boston, after a frantic night of violence that left one MIT police officer dead, an MBTA Transit Police officer wounded, and an embattled public — rattled again by the touch of terrorism — huddled inside homes. 
 
 Tsarnaev’s elder brother and ­alleged accom­plice — 26-year-old Tamerlan Tsarnaev, the second suspect in Monday’s Boston Marathon attack — was pronounced dead early Friday morning at Beth Israel ­Deaconess Medical Center, ­after suffering shrapnel and bullet wounds in a gunfight with police. 
 
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 “It’s a proud day to be a Boston police officer,” Police Commissioner Edward F. Davis told his force over the radio moments after the arrest. “Thank you all.” 
 
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 President Obama, addressing the nation from the White House, ­applauded Boston for not allowing the terrorists to prevail. 
 
 “They failed because the people of Boston refused to be intimidated,” the president said. 
 
 Friday will be remembered as the day the city stood still, after Governor Deval Patrick asked the people of Boston and the nearby communities of Watertown, Waltham, ­Newton, Belmont, and Cambridge to “shelter in place” — stay inside, lock the door, and don’t open it for anyone except police in uniform — while the younger ­Tsarnaev was on the loose. 
 
 A city of some 625,000, in a ­metropolis of 2 million, screeched to a halt. Heavily armed officers patrolled eerily empty streets that looked like the set of an apocalyptic movie. The MBTA halted its trains, buses, and subways. Taxi service was temporarily frozen. Amtrak stopped service between Boston and Providence. Officials asked businesses across the region not to open. The Red Sox and Bruins games were postponed. And the campus of the University of Massachusetts Dartmouth, where ­Dzhokhar Tsarnaev is a student, was evacuated and closed. 
 
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 The day began with bomb blasts and gunshots on a street in Watertown, where police said more than 200 rounds were fired in the battle. 
 
 While his brother was taken to the hospital, where he was pronounced dead, Dzhokhar Tsarnaev survived and escaped on foot. Local, state, and federal law enforcement officers — includ­ing the Secret Service, K-9 teams, ­explosives experts, and SWAT officers — searched door to door for the suspect throughout Friday. Police in ­helicopters scoured the streetscape from above. More than 1,000 officers participated in the hunt. 
 
 By 6 p.m., frustrated officials relaxed the rule and allowed residents to leave their homes. The people of Watertown began to venture outside. 
 
 But within an hour, the crack of gunshots again blasted through the neighborhood. ­Sirens blared, and officers on foot scrambled down Franklin Street. 
 
 Police found Dzhokhar ­Tsarnaev hiding on a boat stored in a backyard on ­Franklin Street. Police ­exchanged gunfire with him before capturing him alive. Spontaneous celebrations erupted across the region, from the ­Boston Common to the Back Bay streets near the bombing. 
 
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 The boat’s owners, a couple, spent Friday hunkered down under the stay-at-home order. When it was lifted early in the evening, they ventured outside for some fresh air and the man noticed the tarp on his boat blowing in the wind, according to their his son, Robert Duffy. 
 
 The cords securing it had been cut and there was blood near the straps. Duffy’s father called police, who swarmed the yard and had the couple evacuated, Duffy said. 
 
 CJ GUNTHER/EPA The ambulance carrying Dzhokhar Tsarnaev left the Franklin Street area. 
 
 Residents, who had barricaded themselves in their homes for nearly 20 hours, were still deeply shaken. “I’m so happy they got these guys,” said Tom Sheridan, 35, an interior painter from Watertown, as he cheered police cruisers and ambulances as they drove by on Mount ­Auburn Street. “But I’m worried there are more people out there like that. It won’t be the same.” 
 
 Tsarnaev was wounded and taken to a hospital. In an interview late last night, Patrick said he is “hoping very deeply he survives those wounds, because I’ve got a lot of questions and I know investigators have a lot of questions for him.” 
 
 Investigators believe the Tsarnaev siblings, originally from the former Soviet Republic of Kyrgyzstan, who came to the United States in the early 2000s, are responsible for the attack on the Marathon on Monday that killed three people and injured more than 170, many grievously. 
 
 The FBI-led investigation of the atrocity took a sudden and shocking turn Thursday afternoon after the FBI released photos and videos of the alleged Marathon bombers and asked the public for help identifying them. The images showed two young men casually lugging backpacks along Boylston Street Monday, shortly before two bombs exploded near the finish line. 
 
 Investigators said they ­believe the suspects carried crude but powerful bombs made from household pressure cookers in their backpacks, which they abandoned on the sidewalk. 
 
 Sean Collier, a 26-year-old MIT police officer, was killed in a late night confrontation with the two suspects behind the deadly Boston Marathon. 
 
 Upon release of the images, tips poured into the FBI. Within hours, the brothers ­allegedly killed again, shooting Massachusetts Institute of Technology police officer Sean Collier in his cruiser, near ­Vassar and Main streets in Cambridge, at about 10:24 p.m. The 26-year-old officer later died. 
 
 Police say the siblings carjacked a motorist minutes later on Memorial Drive. They released the unidentified motorist in Cambridge about 30 minutes later, police said. He was not hurt. Later that evening — the timing is unclear — an ­MBTA police officer spotted the stolen car, and a cavalcade of police cruisers chased the suspects into Watertown. The brothers threw explosives at the pursuing officers, police said. 
 
 The brothers stopped near Dexter and Laurel streets, got out of the car, and traded gunfire with police for several minutes. MBTA Transit Police Officer Richard H. Donohue Jr., 33, was wounded. He was in stable condition Friday at Mount ­Auburn Hospital. 
 
 The elder brother was shot in the battle and collapsed.As his brother lay on the street, Dzhokhar Tsarnaev jumped into the car and took off, plowing past a line of police officers who fired furiously. As he drove, he ran over his brother’s body. Dzhokhar Tsarnaev abandoned the car nearby and fled on foot, triggering an enormous search and setting the region on edge. 
 
 Police took Tamerlan ­Tsarnaev to Beth Israel Deaconess Medical Center about 1:10 a.m. Friday. He was pronounced dead at 1:35 a.m. Dr. Richard Wolfe said the suspect had been hit by shrapnel from an explosion and that he had died from “a combination of blasts” and “multiple gunshot wounds.” 
 
 The question that remains is why the siblings would attack their adoptive nation. But a picture began to emerge Friday of Tamerlan Tsarnaev as an aggres­sive, possibly radicalized immigrant who may have ­ensnared his younger brother — described almost universally as smart and sweet — into an act of terror. 
 
 Johannes Hirn/Landov Tamerlan Tsarnaev is shown inside the Wai Kru Mixed Martial Arts center in Boston in 2009. 
 
 “I used to warn Dzhokhar that Tamerlan was up to no good,” Zaur Tsarnaev, who identified himself as a 26-year-old cousin, said by phone Friday from Makhachkala, Russia. “[Tamerlan] was always getting into trouble. He was never happy, never cheering, never smiling. He used to strike his girlfriend. He hurt her a few times. He was not a nice man.” 
 
 In a photo essay about boxing, Tamerlan said: “I don’t have a single American friend. I don’t understand them.” 
 
 In 2011, a foreign government asked the FBI for information about Tamerlan ­Tsarnaev, based on information that he was a follower of “radical Islam” who had changed drastically, the bureau said in a statement Friday. In response, the FBI investigated and interviewed Tamerlan and family members. “The FBI did not find any terrorism activity, domestic or foreign,” the bureau said. 
 
 Dzhokhar, the suspect seen in FBI photos in a white cap worn backward, was a student at the University of Massachusetts Dartmouth. On Wednesday, two days after the Marathon ­attack, he spent the night at his dorm, according to a school ­official who declined to be named. He was an all-star wrestler and a member of the class of 2011 at Cambridge Rindge & Latin School; he won a Cambridge City Scholarship that year. 
 
 Yearbook photo of Dzhokhar Tsarnaev 
 
 A Northeastern University sophomore who lived within blocks of Dzhokhar and graduated from Cambridge Rindge and Latin with him described the younger bombing suspect as an honor student popular with classmates who enjoyed playing pickup basketball with a large circle of friends. 
 
 Gilberto Junior, 44, owner of Junior’s Auto body in Somerville, said the younger suspect dropped off a white Mercedes station wagon two weeks ago for repairs. Junior said he had not yet touched the car when the suspect came back demanding the car, the day after the bombing. The owner said Dzhokhar appeared nervous. 
 
 The family of 8-year-old Martin Richard, who died in the blasts, thanked law enforcement officers for their work on the investigation. “None of this will bring our beloved Martin back, or reverse the injuries these men inflicted on our family and nearly two hundred others,” the Dorchester family said in a statement. “We continue to pray for healing and for comfort on the long road that lies ahead for every victim and their loved ones.” 
 
 William Campbell III, whose 29-year-old sister, Krystle M. Campbell, was killed when the bombs went off on Boylston Street Monday, said after ­Tsarnaev was captured: “I’m happy that nobody else is going to get hurt by these guys, but it’s not going to bring her back.” 
 
 As for the rest of the family, including Krystle’s father, William Campbell Jr., and mother, Patricia Campbell, “they’re happy they got the guys, but basically they feel the same,” he said. “You can only get so angry, and you then know she’s not ­going to be here anymore.” 
 
 James Vaznis, Andrea Estes, Shelley Murphy, Eric Moskowitz, Maria Cramer, Brian MacQuarrie, Milton J. Valencia, Meghan E. Irons, Matt Carroll, Michael Levenson, Noah Bierman, Scott Helman, Evan ­Allen, Akilah Johnson, Martine Powers, Bryan Marquard, and Brian Ballou of the Globe staff and Globe correspondents Zachary T. Sampson, Derek J. Anderson, Matt Rocheleau, ­Jaclyn Reiss, and Todd Feathers contributed to this report. Mark Arsenault can be reached at marsenault@globe.com ||||| Police patrol through a neighborhood in Watertown, Mass., while searching for Dzhokhar A. Tsarnaev, a suspect in the Boston Marathon bombings. All residents of Boston were ordered to stay in their homes Friday morning as the search for the surviving suspect in the marathon bombings continued after a long night of violence that left another suspect dead. 
 
 April 19, 2013 Police patrol through a neighborhood in Watertown, Mass., while searching for Dzhokhar A. Tsarnaev, a suspect in the Boston Marathon bombings. All residents of Boston were ordered to stay in their homes Friday morning as the search for the surviving suspect in the marathon bombings continued after a long night of violence that left another suspect dead. Charles Krupa/AP 
 
 Following a massive search that shut down the city of Boston and its environs, authorities late Friday apprehended Dzhokhar Tsarnaev, a suspect in the marathon bombings who had been missing since early in the day, when he had escaped from a shootout that had left his brother,and fellow suspect, dead. 
 
 Authorities shot and killed one suspect in Monday’s Boston Marathon bombings, and police were searching for a second suspect who was on the loose in Watertown, Mass., Friday after a chaotic night that left one police officer dead and another critically wounded in the Boston suburbs. 
 
 Authorities shot and killed one suspect in Monday’s Boston Marathon bombings, and police were searching for a second suspect who was on the loose in Watertown, Mass., Friday after a chaotic night that left one police officer dead and another critically wounded in the Boston suburbs. 
 
 WATERTOWN, Mass.— Police said they had taken the second suspect in the Boston Marathon bombings into custody here Friday night, after a day of intense searching that shut down daily life across a large swath of greater Boston. 
 
 Shortly after 8 p.m., police surrounded a boat stored behind a home in East Watertown, a short distance away from where Dzhokhar Tsarnaev, 19, had been last seen. Authorities said they believed Tsarnaev was inside the boat, which had been covered in a tarp. He was thought to be wounded but alive: television crews reported that they could hear police calling his name, attempting to induce his surrender. 
 
 The other suspect in the bombings, Tsarnaev’s 26-year-old brother, Tamerlan, was killed early Friday morning after a shootout with police in another section of Watertown. 
 
 Also Friday, a report from Russian television cited the men’s mother as saying her older son had previously been interviewed by the FBI because of his interest in radical Islamic teachings. The FBI confirmed that agents in Boston had interviewed the elder Tsarnaev in 2011, on behalf of an unspecified foreign government that suspected he had ties to a terrorist organization. But the FBI found nothing warranting further investigation. 
 
 The standoff with the younger Tsarnaev began just minutes after a press conference in which authorities had conceded that a daylong search for Tsarnaev had come up empty. They had said they did not know where the fugitive was, but would still lift a “shelter in place” order anyway. 
 
 “You can get back out, as long as you are vigilant,” said Massachusetts Gov. Deval Patrick (D). 
 
 As night fell again here, the Tsarnaevs had become a new lesson in the awful magnifying power of terrorism. Two unremarkable brothers, armed with low-tech bombs and no apparent escape plan, had allegedly killed four people, injured more than 170, and then held one of America’s great cities in terror for a full day. And counting. 
 
 While law enforcement officers continued to look for Tsarnaev, investigators in Washington and elsewhere began seeking to understand what had turned them to violence. 
 
 The Tsarnaev brothers are of Chechen heritage. Both were born in the Caucusus region, a cauldron fought over by Chechen separatists, Russian security forces, Islamic extremists and organized crime. They had emigrated legally, and lived for years in the Boston area, where their father, Anzor, was an auto mechanic. 
 
 In the past, both men had embraced American passions, according to friends and neighbors. Tamerlan, 26, was an accomplished boxer, with a wife and child. Dzhokhar was a wrestler at Cambridge’s public high school, who went on to attend the University of Massachusetts-Dartmouth. 
 
 On Thursday evening, authorities released photos of two men spotted carrying backpacks near the Marathon’s finish line. These were apparently the Tsarnaevs, though authorities did not say that at the time--and, perhaps, did not know it at all. 
 
 Their targets, it turned out, had not fled the city or the country. A few hours later, they began a violent spree just across the Charles River in Cambridge. 
 
 At about 10:30 p.m., authorities said, the two shot and killed MIT Police officer Sean Collier, 26, as Collier sat in his cruiser. It was unclear what triggered that shooting: authorities said surveillance video appears to show the two approaching Collier and killing him without warning. 
 
 After that, the men allegedly carjacked a Mercedes sport utility vehicle, and took the driver with them. At least one brother told the carjacked driver that they were the marathon bombers. They forced the driver to stop at several bank machines, and took $800 that he withdrew. After a few minutes, the man was left behind at a gas station, unharmed. It was unclear if he escaped, or was let go. 
 
 From there, the brothers drove about three miles, throwing explosives out the window at police. In Watertown, they engaged in a shootout with police, in which at least 200 rounds were fired. 
 
 Authorities said that Tamarlan Tsarnaev left the car at one point, and attempted to throw an explosive at officers. The device, however, went off in his hand. Police then tackled the wounded suspect in the street. Then, authorities said, Dzhokhar Tsarnaev--still behind the wheel of a car, swerved at the officers in an effort to hit them. 
 
 The officers dodged. Tamerlan did not. He was dragged under the car, and later died at a Boston hospital. In the same confrontation, a Boston Transit police officer was also shot and wounded. {{Officials later identified the officer as Richard H. Donahue, 33, who was treated at Mt. Auburn Hospital and released. 
 
 Dzhokhar Tsarnaev escaped. Police later conceded that there were not enough officers to establish a perimeter. The teenager is believed to have fled on foot: police found a small blood trail, indicating he was injured. 
 
 Then he vanished. 
 
 Starting after midnight Friday, an army of police officers and federal investigators began fanning out to look for him. SWAT teams from as far away as Cape Cod and New Hampshire rolled through the streets in armored cars, as police carefully searched house to house in Watertown. 
 
 While they looked, authorities issued a massive order to stay at home. It covered the entire city of Boston, plus the suburban towns of Belmont, Brookline, Cambridge, Newton, Waltham and Watertown. 
 
 “This situation is grave. We are here to protect public safety,” Boston Police Commissioner Ed Davis said in the morning, as the extraordinary lockdown was put in place. “We believe this to be a terrorist. We believe this to be a man here to kill people.” 
 
 As the afternoon wore on, authorities closed down the suspects’ street, and searched their home. President Obama was briefed. The Tsarnaev brothers’ relatives appeared one after another on cable TV, with one uncle denouncing the two as “losers.” 
 
 In Boston, a few people began to defy orders, and come out in the streets. As night fell, the governor said that everyone could do that--but with the frightening knowledge that an alleged killer and bomb-maker was out there, too. 
 
 “We can return to living our lives,” Patrick said. 
 
 While authorities looked for Tsarnaev, another phase of the investigation was already underway. In Washington and elsewhere, investigators interviewed family members, and searched for travel records, financial documents and for the brothers’ traces on Internet. 
 
 For now, the brothers’ alleged motive remains unknown. The Tsarnaevs, like many ethnic Chechens, are Muslim. In the last several months, Tamerlan Tsarnaev had posted videos to YouTube indicating his interest in radical Muslim ideologies. 
 
 Another question: did the men have help, either from within the U.S. or abroad? While militant Chechen groups have been blamed for terror attacks in the past, their target has usually been Russia, a bitter foe from Caucusus wars. 
 
 On Friday, U.S. authorities said they had no proof that anybody beyond the two Tsarnaev brothers was involved in the marathon attacks. But they were not done looking.
– Authorities say one of two suspects in the Boston Marathon bombing is dead and a massive manhunt is under way for the other, who has been identified as 19-year-old Dzhokhar A. Tsarnaev. Boston is effectively shut down in the meantime: Residents of Boston, Watertown, Newton, Waltham, Belmont, Cambridge, and the Allston-Brighton neighborhoods of Boston were told to remain in their homes; mass transit has been halted; businesses were asked not to open; and the Boston Globe reports that at least 16 area colleges have canceled classes. What we know of what happened overnight, per the AP and the Washington Post: The Middlesex district attorney says the two men are suspected of killing an MIT police officer at the college last night after the officer responded to a disturbance, then stealing a car at gunpoint and later releasing its driver unharmed. (All just hours after police released photos of the bombing suspects.) Authorities say the suspects threw explosives from the car as police followed it into Watertown; witnesses reported hearing multiple gunshots and explosions at about 1am. A transit police officer was critically wounded. The suspects and police exchanged gunfire and one of the suspects was critically injured and later died at a hospital while the other escaped. Doctors at Boston's Beth Israel Deaconess Medical Center say they treated a man with a possible blast injury and multiple gunshot wounds. They wouldn't confirm that the patient, who came in with police, was the suspect in the black hat from marathon surveillance footage. Police say the suspect on loose is a "terrorist" who "came here to kill people." Governor Deval Patrick held a press conference with police this morning extending the shelter-in-place warning to all of Boston. "There is a massive manhunt underway," he assured reporters. "We've got every asset that we can possibly muster on the ground right now." Authorities have identified the MIT officer who was killed as 26-year-old Sean Collier of Somerville, according to the Boston Globe. The MBTA police officer who was injured has been identified as Richard H. Donohue.