BOMBING AT BOSTON MARATHON-GRAPHIC PHOTOS

[Duchess]

The Boston Marathon bombing suspects — armed with explosives and guns — battled law enforcement officers in a Boston suburb early Friday morning, unleashing chaos until cops took one of the men into custody and the other fled, law enforcement sources said.

Officials later said the suspect taken into custody died and authorities identified the man on the run as the "white-hat" suspect, referencing photographs released by the FBI Thursday. Authorities warned he should be considered armed and dangerous.

The standoff in Watertown, Mass., erupted shortly after the fatal shooting of a Massachusetts Institute of Technology police officer. A transit police officer was also wounded in the Watertown fire fight, officials confirmed to NBC affiliate WHDH.

Officials in Watertown were warning residents to "stay in their homes and not open their doors unless a police officer is there."

"There is a terrorist on the loose," said one officer at an impromptu press conference at about 4:30 a.m. ET.

The suspect at large — believed to be the man who physically placed the bags containing the homemade bombs which killed 3 and injured 170 on Monday — was described as "dressed in a grey hoodie, light skinned male, brown curly hair."

Law enforcement sources said the suspects have international links and have been in the country legally for about a year.

The suspects approached the MIT officer and shot him in head, the sources said. The two then stole the MIT officer's cruiser, robbed a nearby 7-11 and carjacked a Mercedes SUV, briefly kidnapping the driver, the sources said. At various points, the suspects threw explosives out the window of the moving car.

The dead suspect had an improvised explosive device strapped to his chest and the law enforcement sources warned that the suspect on the run may as well.

Watertown resident Andrew Kitzenberg described the earlier police shoot out outside his house. “They engaged in gunfire for a few minutes,” Kitzenberg told NBC News. “They were also utilizing bombs, which sounded and looked like grenades, while engaging in the gunfight. They also had what looked like a pressure-cooker bomb.”

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