29-year-old Officer Kevin Brennan and two other officers responded to the scene around 9 p.m. Tuesday after there was a report of shots fired near 140 Moore Street.
Once on the scene, they encountered three individuals running from the building.
They chased after one individual that they knew from past encounters, and followed him to the rear of 370 Bushwick Avenue.
They found the suspect, believed to be Lewis "Baby" Ortiz who fired once at officers, striking Officer Brennan in the base of his skull.
Commissioner Kelly believes officers fired one shot in return.
It's not known if the suspect was hit as he fled to the fifth floor of the building.
Officer Brennan was rushed to Bellevue Hospital where he is listed in critical but stable condition. Surgeons removed the bullet which Kelly showed to reporters at the news conference.
Officer Brennan is said to be drifting in and out of consciousness.
Mayor Bloomberg said that Officer Brennan has been a member of the NYPD since July 2005, winning many commendations and awards for his service.
Just six weeks ago he celebrated the birth of a daughter.
Meantime, Ortiz is also wanted for questioning in connection with homicide that happened on New Year's Day.
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