UPDATE: Boston suspect is alive and in custody

FBI boston suspect hat side

By Pete Williams, Richard Esposito, Michael Isikoff and Tracy Connor for NBC News

UPDATE: The Boston Marathon bombing suspect was captured Friday night after police found him in a boat in a suburban backyard following a bloody rampage and daylong manhunt, law enforcement sources said.
Cheers went up from a crowd of police gathered at the scene in Watertown, Mass., where bursts of gunfire had been heard over the course of two hours.
The dramatic turn of events ended five days of terror from the bombing at the marathon finish line, which killed three people, wounded 176 and left the city of Boston on edge.

WATERTOWN, Mass. - Bursts of gunfire erupted Friday evening as police surrounded a boat where the Boston Marathon bombing suspect was believed to be holed up, law enforcement sources said.

MORE: Full coverage from NBC News

The dramatic turn of events began unfolding soon after police said residents could leave their homes even though the suspect was still on the run despite a door-to-door search.

Just before 7 p.m., an unsettling barrage of gunfire was heard on Franklin St. in Watertown, Mass., and dozens of police and armored vehicles sped to the area.

Officials said thermal imaging from helicopters had located someone in a boat in the yard of a home. A senior police official later told NBC News the person was believed to be accused bomber Dzhokhar Tsarnaev, 19.

“Probably been there all day,” the official said.

“He has a full tank of gas on the boat,” a police source said.

About an hour after the first barrage in Watertown, Mass., two more bursts of shots were heard.

Police appeared to have Tsarnaev cornered less than an hour after they announced at a briefing that they were lifting a lockdown order because the all-day manhunt had turned up no sign of him.

Just before the briefing, police released new details about the scope of a bloody overnight rampage that began with the death of a campus security officer and ended with the death of Tsarnaev’s 26-year-old brother, Tamerlan, with a bomb strapped to his body.

Hours after the FBI put out their photos Thursday night, the brothers exchanged 200 rounds with police during a stunning pre-dawn firefight and left behind seven homemade explosives, officials said.

The violence led to an extraordinary shutdown of transportation, schools and businesses in Boston and its surrounding suburbs, with police warning more than a million people to hunker down behind locked doors while SWAT teams fanned out looking for the younger suspect.

Investigators chased leads all day but could not find the suspect, a naturalized U.S. citizen of Chechen origin who grew up in Cambridge after his family moved here a decade ago, seeking asylum.