What to Know Chief James P. O'Neill will succeed Bill Bratton as NYPD commissioner.

As the NYPD's Chief of Department, O'Neill introduced "community policing" tactics in precincts across the city.

Bratton, Mayor de Blasio and O'Neill all credit community policing tactics with helping drop the city's crime rate to record lows.

The architect of the NYPD’s “community policing” program, Chief of Department James P. O’Neill, will succeed Bill Bratton as NYPD commissioner after he vacates his post in September, Mayor de Blasio announced Tuesday.

“Jimmy O’Neill has built a national model for bringing police and the community together to fight crime,” de Blasio said. “As the top-ranking uniformed member of the NYPD, Jimmy has spent each day ensuring that New York City remains the safest big city in America."

O'Neill has served in the NYPD for more than 30 years, de Blasio said, beginning in the New York City Transit Police in 1983.

He was appointed to chief of patrol in 2014. He then became chief of department later that year, when Philip Banks resigned his post.

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As chief of department, O'Neill implemented community policing in precincts across the city. Under the program, officers were assigned to precincts with the goal of engaging the community to create trust between police and residents. The "neighborhood coordination officers" were assigned to precincts in every borough of the city.

In a new community policing program, NYPD officers are getting to know the residents in their neighborhoods through an old-school approach — and it’s helping to bring crime statistics down. Marc Santia walks the beat with two cops in Washington Heights, where residents have warmed to their local cops. Read more about the NYPD’s new plan for neighborhood policing.

Bratton, de Blasio and O'Neill all credit the neighborhood policing initiative with lowering crime across the city.

"Few understand the human side of policing better than Jim O'Neill," Bratton said. "As chief, his innovative NCO program is not only making communities safer, it has brought police and the people together."

O'Neill said the strategy lowers "crime, but not at the expense of losing the vital support of the people we are sworn to protect and serve."

O'Neill is a New York native, born and raised in Brooklyn's East Flatbush neighborhood. He holds a master's degree in criminal justice from John Jay College and has taught criminal justice at CUNY Rockland.

His rise to the NYPD’s top position includes serving as commanding officer of the 25, 44 and Central Park Precincts, the NYPD's website says. He also served as the commanding officer of the Firearms Training Section, the Police Academy, Warrant Section and the Fugitive Enforcement Division.

This is what some people were tweeting about the change at the head of the NYPD: