Five people were shot by a gunman wielding a high-power M4 rifle in a Midtown Manhattan building, with four victims succumbing to their injuries.

       One of the four victims was an off-duty New York Police officer assigned to a Bronx precinct, NYC Mayor Eric Adams said Monday evening.

       Officials identified the others killed in the shooting as two men and a woman, whose names have not been released. A fifth victim, who was critically injured, remains at NewYork–Presbyterian, officials said.

       Off-duty NYPD officer Didarul Islam was the father of two and his wife was pregnant, officials said.

       "Police Officer Didarul Islam represented the very best of our department. He was protecting New Yorkers from danger when his life was tragically cut short today," NYPD said in a statement.

       "We join in prayer during this time of incomprehensible pain. We will forever honor his legacy," NYPD's statement continued.

       An immigrant from Bangladesh, the 36-year-old was on the force for 3.5 years, Adams said.

       "He loved this city, and everyone we spoke with stated he was a person of faith and a person that believed in God and believed in living out the life of a godly person. He embodies what the city is all about," Adams said during Monday evening's press conference.

       This is a developing story. Please check back for updates.

       ABC News' Darren Reynolds contributed to this report.