By Sheldon Alberts and Jonathan Easley - 04/19/13 07:30 PM EDT
One suspect in the Boston Marathon bombings was killed and police remained engaged Friday afternoon in a tense manhunt for a second man, following a bloody overnight shootout that left a police officer dead.
The city of Watertown, Mass., is on virtual lockdown, and police instructed residents in other communities — including the entire city of Boston, Cambridge, Belmont, Newton and Waltham — to remain in their homes.
Law enforcement officials are searching for Dzhokhar Tsarnaev, 19. His brother, Tamerlan Tsarnaev, 26, was killed during a firefight.
"We are asking people to shelter in place, that is stay in place, with their door locked," Massachusetts Gov. Deval Patrick (D) said at a Friday news briefing in Watertown.
"We have got every asset that we can possibly muster on the ground right now ... but we are going to need the public to help us help them stay safe."
Just before Patrick spoke Friday morning in Watertown, busloads of heavily armored police arrived on the scene to assist in the door-to-door operations. Police in armored vehicles ranged through empty suburban streets and the Boston Red Sox canceled a Friday night game at Fenway Park to "support" law enforcement efforts.
The dramatic search began after an initial armed confrontation late Thursday in Cambridge between police and the two men who had been identified just hours earlier by the FBI as the primary suspects in Monday's terror bombing at the Boston Marathon. Three people died and 176 were injured when two bombs exploded near the race's finish line.
Law enforcement officials are searching for Dzhokhar Tsarnaev, 19. Source: FBI
The first confrontation with the terror suspects left one Massachusetts Institute of Technology (MIT) police officer dead. He was identified later Friday morning as Sean Collier, 26.
The two suspects then fled to Watertown in a stolen vehicle — reportedly a black Mercedes SUV — where a second gun battle with police occurred after a chase.
Police said the suspects threw explosives from the vehicle before one of them was gravely injured. Tamerlan Tsarnaev, who the FBI identified publicly in photos earlier Thursday wearing a black baseball cap, died later in a hospital.
“During the course of that pursuit, several explosive devices were discharged from the car at the police officers,” Col. Timothy Alben of the Massachusetts State Police told reporters.
A transit police officer was wounded during the second confrontation. Rapid gunfire could be heard ringing through the streets of Watertown in amateur video shot by a local resident.
Authorities are now conducting a door-to-door search in Watertown for Dzhokhar Tsarnaev, who was shown in photos released by the FBI earlier Thursday wearing a white baseball cap.
"We believe this to be a terrorist. We believe this to be a man who's come here to kill people. We need to get him in custody," Boston Police Commissioner Ed Davis told reporters.
Dzhokhar Tsarnaev is believed to be responsible for planting the second bomb at the Boston Marathon.
The terror suspects' uncle, Ruslan Tsarni of Montgomery Village, Md., told reporters the two men were Muslims and ethnic Chechens who came to the United States as children from Kyrgyzstan.
"If you are alive, turn yourself in, and ask for forgiveness from the victims, from the injured," Tsarni said of Dzhokhar. "He put a shame on the entire Chechen ethnicity."
Dzhokhar's father told The Associated Press that his son is a second-year medical student.
"My son is a true angel," Anzor Tsarnaev said from Makhachkala, Russia. "We expected him to come on holidays here."
The University of Massachusetts Dartmouth said a student registered at the school was one of the marathon bombings suspects.
Boston police said they were working closely with officials in Washington on the case.
“This is a rapidly developing situation,” Davis said. “A lot of information is coming in. We’re working very closely with federal authorities in Washington, and we’re examining all databases and all potential leads. Please be patient with us; we are trying to make this safe as quickly as possible, but this is an ongoing situation.”
At a media briefing Friday morning, police said they had shut down Boston's public transit system and were preventing cars from entering or leaving Watertown. Several local universities — including Harvard, MIT and Boston University — were closed and police told business owners not to open on Friday. Amtrak shut down train service between Boston and Providence, R.I.
Thousands of police officers in heavy armor were fanning out block-by-block in their search through Watertown.
“The situation is grave," Alben said.
Boston issued this alert to all residents: "As this investigation unfolds we are advising all residents, citywide, to shelter in place."
"Our No. 1 priority right now is with these neighborhoods here in Watertown," Alben said. "It may take hours to do this ... For right now, this is about public safety."
In an early afternoon press conference Friday, Alben said there has been “no apprehension at this point,” but that the department is following up on “several new leads that have just developed over the last few minutes.”
Alben said police had covered 60 to 70 percent of the Watertown territory in which they were conducting door-to-door searches, and that a bomb squad would be conducting a controlled explosion at a house in Cambridge it secured earlier in the day “out of an abundance of caution.”
The violent standoff began at about 10:30 p.m. on Thursday after reports of a robbery at a 7-Eleven convenience store in Cambridge, The New York Times reported. The first shots were fired shortly after as police investigated and a police chase ensued to Watertown.
Some outlets have reported that the deceased suspect, Tamerlan Tsarnaev, may have had an explosive device strapped to him at the time of his final showdown with police.
In an interview on CNN, Richard Wolfe of Beth Israel Medical Center, the doctor who treated the suspect, said it was unclear but that the injuries suggest he sustained a “blast injury” that appeared to be from an explosive device that may have contained shrapnel.
"I think the medical examiner will conclusively be able to say that, but there were more than just gunshot wounds," Wolfe said.
The events unfolded mere hours after the FBI released photographs and videos of the two Boston suspects and urged the public to help locate them.
At a Thursday news conference, the FBI released photographs and video of two men wearing baseball caps and carrying backpacks, and investigators said they had video of one of the men leaving his backpack near the site of one of the explosions.
"We consider them armed and extremely dangerous. No one should approach them," FBI Special Agent Rick DesLauriers said in a briefing. "No one should attempt to apprehend them except law enforcement. Let me reiterate that caution, do not take any action on your own. If you see these men, contact law enforcement."
Some of the images showed the two men walking together, which captured the attention of investigators.
The first man identified has a black baseball cap with white lettering and a dark backpack. The FBI did not have video of that man leaving his backpack on the marathon route.
The second man, seen leaving the backpack, was wearing a white baseball cap backward. That man, after leaving the backpack, walked west on Boylston Street on the day of the bombings, the FBI agent added.
Tamerlan Tsarnaev was identified publicly by the FBI in photos on Thursday wearing a black baseball cap. Source: FBI
Authorities had previously said that the explosive devices in the bombings had been made of pressure cookers loaded with BB pellets, shards of metal and ball bearings. Law enforcement officials said the explosives were carried in dark nylon bags.
The FBI made its announcement three days after the deadly attack, and the interim was filled with false reports of suspects and arrests.
Obama traveled to Boston on Thursday to take part in an interfaith memorial service for the victims.
The president promised in his speech that the perpetrators of the attack would be captured.
"Yes, we will find you; and yes, you will face justice," Obama said. "We will find you; we will hold you accountable, but more than that, our fidelity to our way of life, to a free and open society, will only grow stronger."
Dzhokhar Tsarnaev is believed to be responsible for planting the second bomb at the Boston Marathon. Source: FBI
Obama also praised Boston for being resilient in carrying on after the tragedy.
"A bomb can't beat us," the president added. "That's why we don't hunker down. That's why we don't cower in fear. We carry on. We race. We strive. We build, and we work, and we love."
Chechnya, a Muslim enclave in the Caucasus, saw a rise in Islamist militancy when separatists fought for independence from Russia after the fall of the Soviet Union; two Chechen militants detonated bombs packed with metal nuts, bolts and screws in the Moscow subway in 2010, killing at least 40 people.
-—Daniel Strauss contributed to this report.
— This story was posted at 5:50 a.m. and updated throughout Friday.