One suspect in the Boston Marathon bombing is dead, and the city of Boston is on lockdown as police search for the second.  The one died from both gunshots and an explosion that he apparently set off, according to first reports:

The search for one of the Boston Marathon bombing suspects — the man seen wearing a white baseball cap — this morning led to the sudden shutdown of the MBTA’s entire network of commuter rail, bus, and subway services.

State authorities also asked people who live in Watertown, Waltham, Newton, Belmont, Cambridge, and Allston-Brighton to stay home and for businesses in those cities and towns to stay closed. …

The other Boston Marathon bombing suspect, the man seen wearing a black hat in photos released Thursday evening, is dead after firing bullets and launching explosives at police.

“We believe these are the same individuals that were responsible for the bombing Monday at the Marathon,’’ State Police Colonel Timothy Alben said today. “We believe that they are responsible for the death of an MIT police officer and the shooting of an MBTA police officer. This is a very serious situation that we are dealing with.’’

Via Twitchy, the Associated Press has reported that both bombing suspects came here from Chechnya a little over a year ago:

http://twitter.com/#!/AP/status/325198361428893698

http://twitter.com/#!/AP/status/325196873486962688

And they may be brothers:

http://twitter.com/#!/jmartpolitico/status/325198125243461632

I’d take that with a grain of salt for now.  I’ve seen other names floated for the other bomber, too.

Update: According to NBC News, it started with an armed robbery of a 7-11:

With a bomb strapped to his chest, one of the Boston Marathon suspects was killed early Friday after he and his accomplice robbed a 7-Eleven, shot a police officer to death, carjacked an SUV and hurled explosives out the window in an extraordinary firefight with law enforcement, authorities told NBC News.

The second suspect — the one in the white hat in photos released by the FBI — was on the loose, and police ordered people in the Boston suburb of Watertown to stay in their homes and businesses not to open. Boston shut down its buses and subway system for the hunt.

The suspects are brothers with the last name Tsarnaez, law enforcement officials told NBC News. The suspect on the loose is 19 and has a Massachusetts driver’s license, they said. Law enforcement officials told NBC News that both men had international ties, had been in the United States about a year and had military experience.

Not exactly a low profile, but after having your pictures all over every news outlet in America, it’s not exactly surprising to see a panicked reaction.

Update: Also from the NBC report:

Andrew Kitzenberg, who lives in Watertown, said he saw the two men shooting at six police cars from 70 or 80 yards away.

“There was a long exchange of gunfire,” told NBC News in an interview. “They were also utilizing bombs, which sounded and looked like grenades, while engaging in the gunfight,” he said. “They also had what looked like a pressure-cooker bomb.”

Again, we’ll know more when the dust settles, and eyewitnesses might not have the expertise to identify bomb types, especially at night.  Clearly, though, these were not your average stick-up men.

Update: Third man?

Third man has been arrested. He's being called an accomplice, not yet called a suspect, reports NPR's Dina Temple-Raston.

— NPR (@NPR) April 19, 2013

I’m watching WDHD TV’s live coverage, and they are reporting that the pair told their carjacking victim that they were the bombers from the Boston Marathon.

Update:  Mediaite clipped this from a local broadcast, with eyewitness video of the shootout. Listen to how many rounds are fired in this exchange:

http://www.youtube.com/watch?v=uEtDVoXsuEw

Update: One MIT police officer is dead, another police officer wounded, but the story of the carjacking and kidnapping seems odd with those in mind:

About 10:30, police received reports that a campus security officer at M.I.T. was shot while he sat in his police cruiser. He was found with multiple gunshot wounds, according to a statement issued by Middlesex Acting District Attorney Michael Pelgro, Cambridge Police Commissioner Robert Haas, and MIT Police Chief John DiFava. The officer was taken to Massachusetts General Hospital, where he was pronounced dead.

A short time later, police received reports of an armed carjacking of a Mercedes SUV by two males in the area of Third Street in Cambridge, the statement said. “The victim was carjacked at gunpoint by two males and was kept in the car with the suspects for approximately a half hour,” the statement said. He was later released, uninjured, at a gas station on Memorial Drive in Cambridge.

Why leave the driver alive? It allowed the man to alert PD, which led to the shootout.  The other suspect then used the SUV as a battering ram to make his escape:

Meanwhile, Dzhokhar A. Tsarnaev, said Mr. Kitzenberg, got back into the SUV, turned it toward officers and “put the pedal to the metal.” The car “went right through the cops, broke right through and continued west.”

The two men left “a few backpacks right by the car, and there is a bomb robot out there now.” Police had told residents to stay away from their windows, he said.

As of last night, Dzokhar was still relaxed enough to check in on Facebook, apparently:

Profile for Djohar Tsarnaev says he last logged on to the social network at 6:04pm yesterday – pic.twitter.com/BH5kbn5w9k

— Matthew Keys (@MatthewKeysLive) April 19, 2013

Update: Too good to check?

PETE WILLIAMS: Dzhokhar Tsarnaev Drover Over His Brother!

— Joe Weisenthal (@TheStalwart) April 19, 2013

Update: WHDH reports that the two brothers may have come here as young children, as long as a decade ago.  The name of the dead brother has been released, Tamerlan Tsarnaev.

Update: ABC’s Pierre Thomas reports that police are “worried” that other bombs may be planted around the city, and that they may be looking for “associates” that may have been involved.  Police also tell ABC that paramilitary training seems to be part of the Tsarnaev’s background based on how they handled the shootout and the bombing.

Update: Just in case…

A no fly zone has been enacted over #Watertown Mass. This joins a no fly zone already in place over the bomb site.

— ABC News (@ABC) April 19, 2013

Update: Gov. Deval Patrick issues a statement to tell people in the search area to stay inside with doors locked, and not to let anyone enter without a valid law-enforcement ID.  “We have every asset that we can possibly muster on the ground right now.”

The police announced at the same briefing that the “shelter in place” recommendation has been expanded to the entire city of Boston.

Update: This is reportedly Tamerlan Tsarnaev’s YouTube account.  If so (and it’s still unconfirmed), a theme emerges rather quickly.

Update: The extraordinary lockdown continues and is extended to taxi service:

Boston PD: All taxi service in the City of Boston has been suspended pending further notice.

— ABC News (@ABC) April 19, 2013

Plus, confirmation from a family member that the two suspects were brothers:

BREAKING: 3 law enforcement sources, uncle of Boston Marathon bomb suspects confirm men were brothers.

— The Associated Press (@AP) April 19, 2013

And the timing of their arrival:

Update: Boston bombing suspects came to U.S. with their family in 2002 or 2003

— NBC Nightly News with Lester Holt (@NBCNightlyNews) April 19, 2013

So, as Allahpundit asked me in a DM — when were these two radicalized? That may have some significance for policy down the road.

Update: New suspect photo from the BPD:

New suspect photo from @Boston_Police: 19 year-old Dzhokhar Tsarnaev of Cambridge. Considered armed & dangerous. pic.twitter.com/Yq7sMlBQta

— CNN Breaking News (@cnnbrk) April 19, 2013

Update: According to Fox’s live feed, the police have someone cornered in a Watertown house.  Lots of police and SWAT personnel on scene.  Police on bullhorns are yelling, “Come out! Come out!”

Update: Perhaps this was the “third person of interest”?

Person, not a suspect, is in police custody at the house on Norfolk St, where the brothers lived – @NBCNews

— Breaking News (@BreakingNews) April 19, 2013

Update: According to Fox’s live broadcast, the uncle of the two bombing suspects said that both of his nephews are “absolute losers,” and called for Dzhokhar to surrender.  So far, no change on the standoff.

Update: While the standoff continues, this alert just went out in New York City:

https://twitter.com/Breaking911/status/325229955434827776

Could just be caution, could be unrelated, but definitely bears watching.

Update: The FBI released another picture of Dzhokar:

#Breaking: The FBI has just released a new photo of suspect #2 @ABC pic.twitter.com/Gdryq7HPkU

— Gio Benitez (@GioBenitez) April 19, 2013

Update: NPR says that the police are pessimistic about the prospects of taking Dzhokar alive in this standoff:

Law enforcement source: increasingly believes suspect holed up in Watertown acting in way that they may not be able to "take him alive."

— NPR (@NPR) April 19, 2013

Update: The suspects’ uncle may have had no sympathy for his nephews, but their father called Dzhokhar “a true angel“:

“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.”

I think we can cut Dad some slack here.  What a horrible, horrible day it would be for an unsuspecting parent.

Update: Supposedly the BPD is acting on “Internet intelligence” that the suspect is threatening to kill as many people as possible in revenge for his dead brother, but that comes from a Twitter account that is probably fake; it was just created this morning.  I wouldn’t doubt that the suspect is prepared to do that, since his brother had injuries from an explosive device that may have been strapped to his body, so suicide vests are a big possibility.

Update: NBC now says that PD are looking for two other suspects:

JUST IN :Police now looking for two suspects, according to authorities in Boston http://t.co/QyA6oTX2QP

— NBC News (@NBCNews) April 19, 2013

Maybe related to the Niagara Falls story?

Update: Not much happening at the Watertown standoff at the moment, but the Niagara Falls story seems to be resolving itself as unrelated and no issue.  However, PD have sent out an alert for a gray Honda CRV with MA plate 316-ES9 that may be heading to Connecticut.

Update: The Connecticut state police have found the gray Honda CRV flagged in the alert, apparently empty:

UPDATE:  This vehicle has been recovered in Boston. All calls regarding this case should be directed to Boston investigators.

 Sounds as though this may be a false lead.

Update: The car was actually discovered in Cambridge, so it didn’t go far after all.

Update: Probably not a big surprise at this point:

NBC's Richard Engel: Officials are looking at links to Islamic Jihad Union.

— Dylan Byers (@DylanByers) April 19, 2013

That doesn’t mean that they’ve found any ties, of course, but clearly they’re looking that direction for motive and assistance.

Update: This is interesting — Boston PD have allowed taxi service to resume:

From @npr2way: Earlier Friday, officials told taxis stay off the streets of Boston. @Boston_Police now say taxi service has been restored.

— NPR (@NPR) April 19, 2013

On the other hand, they’re currently bolstering their presence at another location in Cambridge, although that could be to deal with an IED that got tossed out during the police chase, which has been a possibility that police are trying to probe.

Update: UMass Dartmouth is on lockdown, and their website says that police are looking for one of their students in connection to the bombing:

“UMass Dartmouth has learned that a person being sought in connection with the Boston Marathon bombing has been identified as a student registered at UMass Dartmouth,” reads a notice on the university’s website.

Curious. Dzhokhar, or an accomplice?

Update: Now apparently police think that the two brothers split up at some point, which would put the earlier report of Dzhokhar driving over his brother to escape into urban-legend status. The second car’s abandonment in Cambridge may mean that the second suspect isn’t actually in the house in Watertown … or  could be.

Stay tuned, and get prepared for a long day.

Update: NPR picks up on a CNN report that the Watertown standoff may be related to an accomplice, not Dzhokhar:

CNN reports it has been told by law enforcement sources that the latest area of Watertown where police have brought in heavy forces and have asked the media to move back is where a possible accomplice of the suspects is located — not fugitive Dzhokhar Tsarnaev.

Note: Allahpundit will take over the breaking-news coverage in a new thread in a few minutes.