NYPD Commissioner Keechant Sewell, the first woman to lead the largest police force in the nation, resigned suddenly Monday, New York City Mayor Eric Adams said.

Sewell, who was appointed by Adams last year, previously served as the chief of detectives for the Nassau County Police Department.

“I want to thank Police Commissioner Sewell for her devotion over the last 18 months and her steadfast leadership. Her efforts played a leading role in this administration’s tireless work to make New York City safer,” Adams tweeted Monday evening. “When we came into office, crime was trending upwards, and thanks to the brave men and women of the NYPD, most of the major crime categories are now down.”

Sewell is also the third Black person to hold the position in the NYPD’s 177-year history. She was with the Nassau police for 23 years, earning her final promotion to chief of detectives in 2020. 

Police Benevolent Association President Patrick Lynch said Sewell will be missed

“In her short time with the NYPD, Commissioner Sewell made a real impact. She took over a police department in crisis and faced tremendous challenges from day one,” Lynch said in a statement. “She cared about the cops on the street and was always open to working with us to improve their lives and working conditions. There are still enormous challenges facing the NYPD. Her leadership will be sorely missed.”

Sewell said in a message to the department she will always support the NYPD.

“While my time here will come to a close, I will never step away from my advocacy and support for the NYPD, and I will always be a champion for the people of New York City,” Sewell said in her memo. 

The reason for Sewell’s departure was not clear or when her final day would be.