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An off-duty NYPD officer chased after a trio of robbery suspects in the Bronx, N.Y., after he was shot in the chest by one of them, authorities say. The officer then fatally shot one of the suspects.

Police Commissioner Raymond Kelly said Officer Ivan Marcano, 27, was sitting in the passenger seat of his car on Harrison Avenue around 6:30 p.m. Wednesday when his girlfriend saw two men robbing a third.

She told Marcano, who got out of the car, pulled out his gun and shield and identified himself as a police officer, Kelly said.

"As soon as he did, one of the suspects fired, striking Officer Marcano in the chest,'' Kelly said Wednesday evening at a news conference with Mayor Michael Bloomberg at the Bronx hospital where the officer was taken.

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The wounded Marcano got back into the vehicle with his girlfriend behind the wheel. She took off to seek medical attention when their car became held up at a red light behind several vehicles, Kelly said. She honked at the cars; the one in front of her, a white Mustang, turned out to be the suspects' getaway vehicle. It jerked forward, hitting a livery cab and then a parked car before going onto the sidewalk where it came to a stop.

'Remarkable display of marksmanship'

Three men got out of the Mustang and started running on foot. Marcano got out of his car, taking cover some distance away. Holding his left hand over his wound, with his gun in his right hand, he approached the men and fired one shot, Kelly said.

He then moved to another location and fired again.

"In a remarkable display of marksmanship and cool under fire, Officer Marcano fired, striking one of the suspects in the head,'' Kelly said.

The man died at the scene. The other men ran off in different directions.

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Marcano followed one of the men, and came across an ambulance, which got him to Bronx Lebanon Hospital, Kelly said.

A gun was recovered at the scene.

"There's police standing on every corner, all day and every day," said neighbor Crystal Lopez. "So for something like this to happen in police presence is scary."

The group COP SHOT has posted a $10,000 reward for information leading to the arrests and convictions of the two suspects on the loose.

Marcano, who joined the force in 2007 and was assigned to Transit District 12, is expected to be alright.

He is the 12th NYPD officer to be shot in eight separate incidents so far this year, according to Kelly, and the second shooting of a police officer this week. On Tuesday, Nassau County Officer Arthur Lopez was killed after getting shot in what had started out as a traffic stop near the Belmont Park racetrack.