By Donna Leinwand Leger and William M. Welch
USA Today

BOSTON - One of the suspects wanted in Monday's Boston Marathon bombing was shot and killed by police while a second suspect was at large and being pursued, the head of the Massachusetts State Police said early Friday.

Colonel Timothy P. Alben, Superintendent of the Massachusetts State Police said the first suspect from Monday's bombing was shot and killed by police following a pursuit that began Thursday night in Cambridge and ended a short time later in nearby Watertown.

Alben said the second suspect, seen in photographs distributed by the FBI as wearing a white cap, is still at large. He said people should be on the lookout and that officials consider him a suspect.

He did not identify them by name.

Police exchanged gunfire with suspects in a nearby suburb early Friday after a college police officer was shot and killed, authorities said. Police said one of the suspects was shot dead and another was at large.

Police Commissioner Ed Davis said in a Twitter statement that one of the suspects in the Boston Marathon bombing on Monday, seen pictured wearing a white hat, was at large and that another suspect was dead.

Davis told reporters the man they are seeking is armed and dangerous. He urged people to stay in their homes and drew the first official link between the overnight police pursuit and the search for suspects in the Boston Marathon bombing.

"We believe this to be a terrorist. We believe this is a man who came here to kill people. We need to get him in custody,' Davis said.

There was a massive police response, first in Cambridge, where a Massachusetts Institute of Technology police officer was fatally shot in his squad car, the Middlesex District Attorney's office said. A second police officer was wounded a short time later, officials said.

The Boston Globe reported they had captured one of the men wanted in connection with the marathon bombing Monday.

The district attorney's statement said police responded to reports of an armed carjacking by two males who held a victim at gunpoint for half an hour before being released uninjured.

The statement said one suspect was critically injured during the pursuit and later was pronounced dead at a hospital.

A massive police response, including FBI agents and the National Guard, was seen in the post-midnight hours in the city of Watertown, with gunshots and explosions heard, following the shooting death of a campus police officer at MIT in nearby Cambridge.

Police could be seen with guns drawn one one man face down on a paved street. But there was widespread confusion about the events, and police agencies provided little official information.

The confrontation came after a Massachusetts Institute of Technology campus police officer was shot and killed around 10:30 p.m. Thursday night at the school's campus, authorities said.

The Globe cited an official with knowledge of the investigation as saying one suspect in the marathon bombing had been captured and another remained on the loose after the Watertown firefight.

The Massachusetts State Police issued a Tweet at 3:45 a.m. saying police "will be going door by door, street by street, in and around Watertown. Police will be clearly identified. It is a fluid situation.''

The state police also advised residents in and around Watertown to stay inside. "Do NOT answer door unless it is an identified police officer,'' the department said.

FBI spokesman Jason Pack said the FBI was aware of the developments but shed no light on who was in custody or any connection between the bombings on Monday and the developments overnight. "The situation is ongoing. We are working with local authorities to determine what happened,'' he said.

CNN showed video of one man, stripped of his clothes, presumably as a safety precaution, being placed in the back of a police squad car. The Globe reported seeing one man being questioned by FBI agents in an ambulance.

The rapidly moving events unfolded overnight as the entire Boston metro area was on high alert following Monday's fatal bomb explosions during the Boston Marathon and as the FBI was leading a massive manhunt for suspects. The developments came on a day when the FBI issued photographs of two men that it said it is seeking and were seen in surveillance video carrying backpacks in the marathon race crowd on Monday before the twin explosions.

It was not known if the Watertown events were related to the MIT shooting or the fatal explosions earlier in the week. But police response was massive with armored SWAT-type vehicle present as well as FBI and National Guard personnel.

Video from WCVB-TV showed police officers with guns drawn and apparently giving orders to a man face down on the street in Watertown.

An explosion could be heard, and police ordered journalists and spectators to move far back. Multiple police agencies were represented at the scene. Officers said they were looking for another suspect.

"I heard sirens, then a ton of gunshots.,'' said Adam Healy, 31, a behavioral specialist for autism who lives less than a mile from the scene. "And then I heard an explosion amid the gunshots. After the explosion, the sky lit up. "

Dan MacDonald, 40, sitting in a second story Watertown apartment, said he first heard sirens, then gunshots.

"It was about 10 to 15 shots. then there was an onslaught," he said. "There were 25 to 60 shots within 45 seconds. Then the shots stopped and boom. It was like dynamite."

After a loud boom, police pushed spectators and media back more than 200 yards from the scene. More Boston Police in armored vests arrived, along with a special operations truck, SWAT vehicle and police dogs.

Police told residents to stay in their homes.

Stephanie Guyotte, spokeswoman for the Middlesex District Attorney's office, said the situation in Watertown was still unfolding and she had no information on the suspects.

Police in Cambridge, where the school is located, issued a pair of Tweets saying that a campus officer reported shot around 10:30 p.m. had died.

"Police, DA Investigating Fatal Shooting of Campus Police Officer In Cambridge,'' the department Tweeted.

Massachusetts State Police said it was assisting Cambridge and campus police in their investigation.

State police said no one had been arrested.

MIT campus police referred a caller to the campus news bureau, where no one answered calls. MIT posted on its website shortly before 2 a.m. that police advised that the suspect in the officer's death was no longer on campus.

State police spokesman Dave Procopio said the shooting took place about 10:30 p.m. local time outside an MIT building. The injured officer was described as a male but no further information about him was released.

Procopio says authorities are searching for a suspect or suspects.

About 11,000 people attend the school. The MIT campus is in Cambridge, just across the Charles River from Boston and less than two miles from Copley Square, where two bombs exploded Monday near the finish line of the Boston Marathon, triggering a massive manhunt for what the FBI said were two suspects.

Contributing: Melanie Eversley and Yamiche Alcindor in Boston

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