Oleg Tcherniak slashed the officer after knocking an elderly man to the ground, sources said.
The sergeant had found men stripping a car before he was threatened with a knife, police said.
The officers were responding to a domestic violence call when the teen shot at them, police said.
Officers had seen Wilvinson Diaz shoot a 21-year-old man, officials said.
Police believe the man attacked four people with a hammer in Manhattan this week.
David Baril's neighbors said his mental health had been deteriorating for years.
The gun was stolen with 23 other weapons from a bait and tackle shop in Perry, Georgia, police said.
NYPD officer Brian Moore was shot in the head by Demetrius Blackwell, officials said.
Jonathan Efraim, 30, opened fire inside the Irish Hillside Inn, 168-02 Hillside Ave., police said.
The mural on Post Avenue is steps from where John Collado was shot by an undercover officer.
Officer Andrew Dossi was transferred to Mt. Sinai Hospital on Monday morning.
Officer Aliro Pellerano was released from St. Barnabas Hospital to cheers from colleagues.
The shooter was arrested near East Tremont Avenue and Westchester Avenue, sources said.
The mother of the man who shot two NYPD officers offered her condolences to their families.
NYPD officers Wenjian Liu, 32, and Rafael Ramos, 40, were mourned one day after they were shot dead.
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