- Bratton served as NYPD commissioner in the 1990s and resumed the role in 2013
- It's unclear why he is stepping down now
(CNN)The leader of the nation's largest police department is stepping down.
New York Police Commissioner William Bratton, who served in the same role in the 1990s, announced on Tuesday that he will retire in September. He will then become senior managing director and executive chairman of Teneo Risk, a division of the CEO advisory firm Teneo Holdings, the company said in a statement.
James O'Neill, who rose through the ranks to become the NYPD chief of department, will be the next commissioner, Mayor Bill de Blasio said at the new conference.
Bratton's departure comes at a time of record declines in crime but heightened distrust of police by minority communities. The death of Eric Garner, who died at the hands of police on Staten Island in 2014, sparked protests in New York and across the nation.
"The issue of race and community -- we're on a journey but it's not a journey unique to New York City," Bratton said. He added that the department has pushed training to deescalate violent encounters with the public and reduced use of force and civilian complaints.
"It's a crisis in America at this moment," Bratton said. "I would argue that we are farther along in New York City than most places."
Bratton is also stepping down amid an ongoing federal corruption investigation involving high-ranking officers and City Hall demonstrations in which participants this week called for greater police accountability and Bratton's firing.
De Blasio denied any connection between the corruption probe or the protests and the commissioner's departure.
Leaving on high note
Bratton, who has also led police departments in Los Angeles and Boston, is retiring after retaking the NYPD helm in December 2013. When he returned, crime rates were low, but tensions with the community were high because of his predecessor's controversial stop-and-frisk policy that critics said targeted minorities.
Bratton wasn't forced out, two city officials told CNN. He had told friends that he intended to stay about two years and is leaving on his own accord, the officials said.
According to the officials, Bratton is departing on a high note, with crime rates declining, relations with the community improving and the rank and file better trained and equipped than ever before.
"The unfinished business here is ... how do we take this extraordinary organization... forward to meet the issues that America is facing today -- the mistrust of the criminal justice system, particularly by our minority communities, the immigration issues that are so paramount at the moment, the anger directed at our muslin community," Bratton said Tuesday.
"I believe in New York City were are better prepared that anyplace else in America."
Bratton's time at the NYPD
Bratton is credited with pioneering the NYPD's CompStat, a command and accountability system that employed real-time intelligence, rapid deployment of resources and accountability systems in police work.
He also was in charge of the NYPD during the largest crime reduction in New York City's history, de Blasio said at the time of Bratton's return as commissioner in 2013.
Under Bratton's leadership in the mid-1990s, felony crime in New York City fell by 39%, city officials said.
Bratton also led the Los Angeles Police Department, helping bring about a 26% decline in violent crime in his first three years in the top job. By 2009, the crime rate was 54% lower than it had been during his predecessor's final year. He also was praised for improving the LAPD's relationships with the city's many diverse communities.
Bratton also was chief of the New York City Transit Police and Boston police commissioner.
"In life ... if things are going well, it's never a good time to leave, but there's a right time," Bratton said last week. "And whether it's personal life, professional life, that's something in my life I always try to do."
When Bratton was introduced as New York City police commissioner for the second time in late 2013, the law enforcement veteran held up a children's book with the title, "Your Police."
"We must always remember that whenever you see a policeman, he is your friend," said Bratton, reading a passage from a book he first checked out of the library 56 years ago.