A Nassau County police officer was killed Saturday night in a friendly fire incident after an MTA officer shot at him.

Officer Geoffrey Breitkopf — 40 years old, a 12-year veteran and married father of two — was responding to a call from a resident scared of a knife-wielding neighbor. After cops killed the suspect, Breitkopf came to the scene armed but in plainclothes, and an MTA officer shot him. The MTA officer is on sick leave.

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