Here's what we know so far:
1. One suspect is at large; one suspect is dead.
2. These are the alleged Boston Marathon bombers. Last night, authorities released images of the two suspects in Monday's bombings, which killed three people and wounded more than 180 others. Boston Police confirmed early Friday morning that the two men were tied to the attacks.
3. The two suspects have been identified as brothers, American citizens whose family emigrated to the United States from Chechnya, Russia: Dzhokhar Tsarnaev (at large) and Tamerlan Tsarnaev (deceased). They had been living in Cambridge, Massachusetts, for several years.
4. Despite initial reports, the suspects did not rob a 7-Eleven Thursday night. This began when the suspects allegedly shot a MIT campus police officer in his car around 10:30 p.m. The 26-year-old officer, who died of his injuries, has been identified as Sean Collier.
5. The suspects carjacked a Mercedes-Benz SUV and drove to Watertown, Massachusetts, after they shot the MIT campus police officer. The suspects bragged to the car's driver that they were the marathon bombers. The brothers began the night driving a Honda Civic, which they used to hijack the SUV.
6. When Watertown police spotted the car and tried to pull it over, the suspects fled, throwing explosives out the window at officers. They exchanged gunfire with police during the chase that followed, and a Boston transit police officer was shot and wounded. Witnesses in Watertown reported hearing multiple gunshots and explosions early Friday morning.
7. Tamerlan Tsarnaev was fatally shot when he ran toward Watertown police officers and attempted to set off an IED that was strapped to his chest. He died soon after he arrived at Beth Israel-Deaconess Medical Center.
8. Dzhokhar Tsarnaev escaped police capture by driving the SUV through a line of police officers. NBC News reports that he drove over his brother as he fled the scene.
9. The city of Boston was on total lockdown from early Friday morning until 6:10 p.m.. Businesses and schools closed for the day. Officials suspended all mass transit. Boston residents were told to stay in their homes until the suspect was caught. The city's streets were deserted.
10. Reports of shots fired in Watertown, Mass. as of 7:00 p.m.
Here's how it happened:
Boston police battled the two suspects in the Boston Marathon bombings as a manhunt turned into a chaotic and deadly shoot-out Friday morning in nearby Watertown, Massachusetts, according to state and local officials and social media reports.
"We believe this to be a terrorist. We believe this to be a man who has come here to kill people," Boston police commissioner Ed Davis told reporters at a press conference held after 4 a.m. Friday in a mall parking lot. Friday morning, the Associated Press and NBC reported that the two men were brothers and legal residents from the Russian region of Chechya and that one, Dzhokhar Tsarnaev, 19, was still at large.
The overnight battle, which began at the Massachusetts Institute of Technology, came just five hours after police and federal authorities released images of two men, wearing baseball caps, in the minutes before and after the bombing, prompting a vast national hunt.
Mass. State Police Superintendent Colonel Timothy P. Alben told reporters last night's incident began with a robbery at a 7-Eleven convenience store [NOTE: This was later proven not to be true].
An MIT campus police officer died after being shot multiple times Friday evening, according to a statement from the City of Cambridge.
After the shoot-out at MIT, the two suspects then carjacked a Mercedes SUV, Alben said at the press conference. They held the driver, then released the driver, "shaken up but physically unharmed," the local television station WCVB reported.
The suspects told the carjacking victim that they were the marathon bombers, NBC News reported.
"Several explosive devices were discharged from the car at the police officers," Alben said.
"One of the suspects was struck and ultimately taken into custody," he said. "The second suspect was able to flee from that car."
A witness in Watertown, Andrew Kitzenberg, told The New York Times that he saw two men in jackets exchanging "constant gunfire" with police officers. A police SUV "drove towards the shooters" and was shot until it was badly damaged and rolled out of control, hitting two cars in his driveway, Kitzenberg said.
The two shooters then threw a large bomb that looked "like a pressure cooker," which then exploded, he said.
One suspect was tackled by police, Kitzenberg told the Times. The other got back into the SUV and drove directly at officers. The car "went right through the cops, broke right through and continued west," he said.
NBC News reported that the suspect in the car "drove over" the other suspect as he made his escape.
Police named the suspects in the bombing and the frantic Watertown chase as Dzhokhar Tsarnaev, 19, and his older brother Tamerlan Tsarnaev, according to the Associated Press and NBC News.
An official said that "tactical teams" from at least four agencies were pursuing the second suspect, a "light-skinned or caucasian male with longer brown curly hair," who matched the description of a man at the bombing scene in a white hat, on foot in Watertown Friday morning.
"He should be considered armed and dangerous and is a threat to anybody who might approach him," Boston police commissioner Ed Davis told reporters.
Speculation on Reddit and Twitter suggested that a suspect could be an American college student who had been reported missing, but NBC reporter Pete Williams, a consistently reliable source through the week in Boston, reported early Monday morning that the suspects had "overseas military training."
"Law enforcement sources said the suspects have international links and have been in the country legally for about a year," NBC reported.
The suspect was brought to Beth Israel Deaconess Hospital Medical Center, where hospital CEO Kevin Tabb official described the slain suspect at a press conference as an "adult male" who was brought in by the "large police presence."
The doctor who treated the suspect, Dr. David Schoenfeld, would not say what was done for the patient once he arrived at the hospital. A second doctor, Richard Wolfe, described the man as suffering from "blast and potentially gunshot wounds ... probably a blast injury [and] possibly shrapnel" throughout his trunk.
"We don't have any identity on the name of the deceased patient," Tabb said.
Chaos in Watertown
Kitzenberg, also tweeted the police hunt that led through his backyard and put a bullet hole through his wall.
Officers went house to house and yard to yard in Watertown Friday morning, and WCVB reported just before 6:00 a.m. that officers with guns drawn surrounded and entered a house on Dexter Avenue in Watertown, before moving on.
Another man was detained, stripped naked, and searched by the FBI, the journalist Seth Mnookin reported on Twitter. That suspect "end[ed] up being released. Apparently wrong place/time."
MIT issued a statement early Friday mourning the death of the university police officer: "MIT is heartbroken by the news that an MIT Police officer was shot and killed in the line of duty on Thursday night on campus. Our thoughts are now with the family."
Watertown is a town just to the west of Cambridge, across the Charles River from Boston.
Watertown Police Chief Edward Deveau and other officials at a news conference just before 6 a.m. said the businesses were asked to stay closed in Watertown and that people need to stay inside in Watertown, Cambridge, Newton, and Waltham. All Metropolitan Boston Transit Authority service also is suspended until further notice, an official said.
Harvard University, in nearby Cambridge, also canceled classes Friday.
Police scanner reporting shots fired in Watertown, Mass.
Suspects are throwing explosives at officers:
The police scanner reports that two officers are down:
The police scanner also reports that one suspect is in custody and one is down on the ground.
UPDATE — April 19, 2013, 1:19 a.m. EDT: Photos from the scene.
UPDATE — 1:24 a.m.: Police yelling second suspect in custody.
UPDATE — 1:32 a.m.: Correction the second suspect is still outstanding.
UPDATE — 1:45 a.m.: Bomb squad is on the scene.
UPDATE — 1:50 a.m. EDT: First report of a pressure cooker bomb.
UPDATE — 2:17 a.m.: National Guard, FBI, and more Boston Police arrive on the scene.
UPDATE — 3:52 a.m.: Reuters and Getty documented the chase.
UPDATE - 4:10 a.m.: Police confirm one suspect is dead.
Update: 4:35 a.m.: Police released a picture from 7-11 surveillance tape of the suspect who is still at large.
Update — 5:03 a.m.: NBC's Pete Williams reports the suspects had "overseas military training" and had been here "about a year."
Update - 6:42 a.m.: The Associated Press reports that the suspects are Russian.
Update - 6:47 a.m.: Boston Police Department advises residents to stay indoors. Classes have been cancelled at various schools.
Update - 6:51 a.m.: NBC News reports that the suspects are brothers.
Both are legal permanent residents of the United States. The suspect still at large is 19 years old.
Update 6:56 a.m.: The Associated Press and NBC News name the suspect.
Update - 7:13 a.m.: Images of the suspect from his social media page.
Update - 7:45 a.m.: The suspect's brother has been identified as Tamerlan Tsarnaev.
NBC reports that the Tamerlan Tsarnaev is 26 years old, which matches this MA voter's registration.
Update - 7:59 a.m.: Authorities have released a new Wanted poster for the suspect currently at large.
Update - 8:00 a.m.: Police have arrived at 410 Norfolk Street — the house where the suspects are believed to have lived.
Boston Globe reports:
A bomb squad has arrived on Norfolk Street between Cambridge and Webster streets in Cambridge near Inman Square, where the Marathon bombing suspects reportedly lived. State Police and the FBI had blocked off the area earlier this morning, and police escorted residents from their homes and scoured the area around the suspects' apartment.
Update - 8:15 a.m.: In a press conference, Governor Deval Patrick says all Boston residents should shelter-in-place.
Update - 8:49 a.m.: Police have surrounded a house in Watertown and have also taken an unidentified person into custody.
Update - 8:55 a.m.: Two people are now in custody.
Update - 9:06 a.m.: Suspects' uncle: "They do not deserve to exist on this earth."
Update - 9:10 a.m.: WGRZ news reports that two Russian nationals have been stopped at Niagra Falls.
Update - 9:17 a.m.: The FBI has released a new image of the suspect.
Update - 9:24 a.m.: The father of the suspects has given a statement to the Associated Press.
MAKHACHKALA, Russia (AP) — The father of the suspects in the Boston Marathon bombing claims that his son who is still on the loose is a smart and accomplished young man.
Anzor Tsarnaev spoke with The Associated Press by telephone from the Russian city of Makhachkala on Friday after police said one of his sons, 26-year-old Tamerlan, had been killed in a shootout and the other, Dzhokhar, was being intensely pursued.
"My son is a true angel," the elder Tsarnaev said. "Dzhokhar is a second-year medical student in the U.S. He is such an intelligent boy. We expected him to come on holidays here."
Update - 9:25 a.m.: President Obama will be briefed on the situation at 9:30.
Update - 9:28 a.m.: The city of Boston is on total lockdown.
Update - 9:40 a.m.: Police in three states are on the lookout for a Honda CRV with Massachusetts license plate number 36Es9.
Update - 9:43 a.m.: The officer killed in last night's shoot-out has been identified.
Update - 9:47 a.m.: Boston bomber's friend describes his classmate: “He was literally among the sweetest, most laid back guys I've ever known.”
Update - 9:51 a.m.: Boston hospitals are locked down.
Update - 10:01 a.m.: Police think the suspect may be wearing an explosive vest.
Update - 10:08 a.m.: All public transportation service in Boston has been suspended.
Update - 10:11 a.m.: At Niagra Falls, police are telling residents to keep away from the Massachusetts vehicle they stopped earlier.
Update - 10:15 a.m.: WCVB reports that the suspect at large is a student at UMASS Dartmouth and was seen there after the bombings this week.
Update - 10:21 a.m.: President Obama met with his national security team in the White House Situation Room for a briefing on the investigation.
President Obama and top aides met Friday morning in the Situation Room for updates on the developing situation in Boston. Vice President Biden and Attorney General Eric Holder also attended the running briefings.
Update - 10:43 a.m.: Officials concerned that the suspects' house may be booby-trapped.
Update - 10:50 a.m.: The Associated Press reports that the SUV linked to the suspects has been found.
Update - 11:15 a.m.: People are pretending to be the suspects on Twitter. These accounts have been proven to be fake.
Update - 11:28 a.m.: Chechen president releases a statement online: “Any attempt to draw a connection between Chechnya and Tsarnaevs — if they are guilty — is futile.”
Any attempt to draw a connection between Chechnya and Tsarnaevs — if they are guilty — is futile. They were raised in the United States, and their attitudes and beliefs were formed there. It is necessary to seek the roots of this evil in America. The whole world must struggle against terrorism — that we know better than anyone else. We hope for the recovery of all the victims, and we mourn with the Americans.
Update - 11:38 a.m.: BBC reports that the suspects' father believes his sons were framed by the special services for being Muslim.
BBC Monitoring reports that a man named Anzor, who said he was Tamerlan and Dzhokhar Tsarnaev's father, told Russia's Interfax news agency his children were framed.
"The special services framed my children because they are believing Muslims," he was quoted as saying. "Why did they kill Tamerlan? They should have taken him alive. The younger one is now on the run; he was studying in his second year at a medical institute in the US. We were expecting him home in the holidays. Now I don't know what will happen."
Update - 11:40 a.m.: Russian president Vladimir Putin has released a statement.
MOSCOW (AP) — Russia's President Vladimir Putin has called the Boston Marathon explosions a "disgusting" crime.
Putin has offered assistance in investigating Monday's twin bombings in Boston that killed three people and wounded more than 170, saying in a condolences note Tuesday that the international community should come together to fight terrorism.
He followed up on that Thursday while opening the Ice Hockey Under 18 World Championship in Sochi, Russia's Black Sea resort that will host the 2014 Winter Olympics.
Speaking before the game of Russian and U.S. teams, Putin called for a moment of silence and offered condolences. He said that the fact that the Boston attack occurred during a major sports event made it "particularly disgusting."
Russian officials have pledged to do everything necessary to ensure security of the Sochi Games.
Update - 11:40 a.m.: Secretary of State John Kerry: "We've been in a direct confrontation with evil."
John Kerry Not Talking About Chechnya Ties To Boston Bombing:
Secretary Of State steers clear of foreign policy implications after Boston bombings.
Update - 11:46.am.: The FBI has issued a new Wanted poster for Dzhokhar Tsarnaev.
Update - 12:03 p.m.: Ruslan Tsarni, the Boston bombing suspects' uncle, has denounced his nephews in an angry impromptu press conference.
Update - 12:12 p.m.: A high school classmate of Dzhokhar Tsarnaev confirms to BuzzFeed that @J_tsar is his Twitter account.
Update - 12:48 p.m.: Amtrak has suspended all service from NY - Boston.
Update - 1:03 p.m.: Massachusetts Police announce that there will be a controlled explosion at the suspects' home on Norfolk Street, Cambridge.
Update - 1:40 p.m.: Sister of alleged bombers speaks to press, FBI.
Twenty-six year-old Alina Tsarnaeva spoke to the Newark Star-Ledger before FBI agents arrived at her West New York, New Jersey apartment:
"They were great people. I never would have expected it," said the woman, of the suspects in Monday's bombing. "They are smart – I don't know what's gotten into them."
Through a slight crack in the door of a West New York apartment this morning, the woman answered a few questions. She referred to Dzhokhar A. Tsarnaev, 19, and his brother Tamerlan, 26, as her own "brothers."
Alina Tsarnaeva told reporters that she had not seen either of her brothers in years and referred to Dzhokhar Tsarnaev — who is still at large — an "amazing child."
"No I'm not OK — no one is okay right now," she said. "I'm hurt for everyone who has been hurt. I'm sorry for all the people who are hurt and for all the people who lost their lives."
Update - 1:45 p.m.: ABC reports that 15 police officers were injured in Thursday night's firefight.
Update - 2:00 p.m.: Connecticut and Massachusetts police have issued a new bulletin looking for a Green Honda Civic.
Update - 2:27 p.m.: Suspected bombers' aunt tells press she is suspicious that the attacks were staged.
Update - 2:30 p.m.: Massachusetts Police report that they have the Honda Civic in their possession.
Update - 2:42 p.m.: The White House releases an image of President Obama meeting with his national security team to discuss the Boston investigation.
Update - 3:06 p.m.: CBS News reports that Dzhokhar Tsarnaev was seen yesterday in his dorm room at UMass Dartmouth yesterday afternoon.
Anthony Mason of CBS reports that he talked to a friend for 10 minutes in his dorm room around noon on Thursday. He drove off later in a green Honda Civic, telling his friend that he "had things to do."
Update - 3:12 p.m.: Boston police have postponed public events planned for Friday night.
Update - 3:22 p.m.: In a live interview, the suspects' father tells CNN that "someone framed" his sons.
Anzor Tsaraev: "Someone framed them. I don't know who exactly did it, but someone did. And being cowards, they shot the boy dead. There are cops like this."
CNN reported that the interview was cut short because Russian authorities took the suspects' father away.
Update - 3:48 p.m.: New pictures have emerged of suspected bomber Dzhokhar Tsarnaev at the Boston Marathon on Monday. One image shows 8-year-old bombing casualty Martin Richard, Dzhokhar and an unattended backpack before the explosion.
Dzhokhar appears to have stuck around to watch the aftermath of the bombings.
Update - 4:17 p.m.: NBC News reports that 7 IEDs have been recovered so far in the investigation.
The homemade explosives were discovered in Watertown and in the suspects' house in Cambridge.
Update - 4:43 p.m.: Massachusetts state police issue a correction about the suspects' car via Twitter.
Update - 5:10 p.m.: The Boston Globe has discovered an eerie image of the two suspects watching the Boston Marathon's finish line.
Update - 6:10 p.m.: The "stay indoors request" has been lifted, but Mass. Gov. Deval Patrick cautions residents to "remain vigilant."
Update - 6:35 p.m.: INTERPOL has issued a global security alert in connection with the Boston marathon bombings at the request of U.S. law enforcement authorities.
Update - 6:44 p.m.: FBI interviewed dead suspect Tamerlan Tsarnaev two years ago at the request of a foreign government.
The FBI admitted Friday they interviewed the now-deceased Boston Marathon bombing suspect Tamerlan Tsarnaev two years ago and failed to find any incriminating information about him.
As first reported by CBS News correspondent Bob Orr, the FBI interviewed Tsarnaev, the elder brother of at-large bombing suspect Dzhokhar A. Tsarnaev, at the request of a foreign government to see if he had any extremist ties, but failed to find any linkage.
Update - 6:55 p.m.: Reports of shots fired in Watertown, Mass.
Update - 7:03 p.m.: Boston Police reports of police operations in Watertown.
Update - 7:06 p.m.: Multiple sources reporting that police have "pinned down" the terror bomb suspect.
Update - 7:15 p.m.: Boston police advise residents to stay inside.
Update - 7:19 p.m.: Unconfirmed reports that the suspect is "down."
It is unclear whether he is dead or alive. Will update as information is available.
Update - 7:25 p.m.: NBC News is reporting that a body has been found. BuzzFeed cannot confirm this report.
Update - 7:53 p.m.: Conflicting reports.
More detailed information about the standoff can be found here.
Update - 8:03 p.m.: Boston Globe reporter tweets from outside the house.
Update - 8:16 p.m.: Multiple sources confirm that the boat is on fire.
Firefighters on the scene.
Update - 8:18 p.m.: NBC reports that the suspect is covered in blood.
Update - 8:30 p.m.: Multiple sources report that a negotiator has arrived on the scene.
Suspect believed to be alive.
Update - 8:34 pm.: Reports that 3 college age people have been taken into custody.
Update - 8:43 p.m.: MULTIPLE reports that the suspect is in custody and alive.
Update - 8:45 p.m.: BuzzFeed can confirm that Dzhokhar Tsarnaev is alive and has been taken into police custody.
The suspect is in police custody and an ambulance is en route to the scene.