As William Bratton gets set to embark on his second tour of duty as New York City police commissioner, he will find a very different city than the one he left behind nearly 20 years ago.

The NYPD now has a robust counterterrorism unit born in the days after the Sept. 11 attacks. A drop in crime, which began under Bratton in 1994, has intensified to record lows.

And Bratton inherits a department that is under intense scrutiny for its use of stop-and-frisk, a policing tactic he has utilized in every stop in his decorated career.

Further complicating matters for Bratton is that one of stop-and-frisk’s most vocal critics, Mayor-elect Bill de Blasio, is the man who is giving Bratton a second shot at running the nation’s largest police force.

While unveiling his choice of Bratton on Thursday, de Blasio insisted that the new commissioner was the right man to further the city’s public safety gains while improving police-community relations. He also downplayed statistics that show that the number of stops surged during Bratton’s tenure as head of the Los Angeles Police Department between 2002 and 2009.

“The community came to understand that the stops that were necessary were being done for a good reason,” de Blasio said. “There was that communication, that sense of legitimacy, and an appreciation.”

The tactic allows police to stop anyone acting suspicious. Its supporters, like outgoing Mayor Michael Bloomberg and Police Commissioner Raymond Kelly, believe it has driven down crime, while its critics believe it unfairly targets minorities and has splintered relations between police and communities of color.

“The overuse of stop and frisk, the unconstitutional use of stop and frisk, the targeting of young men of color regardless of whether they had done anything wrong, that’s going to end,” said the mayor-elect, a Democrat, who takes office Jan 1. “We’re not going to proceed with a policy where hardworking, law-abiding young men of color are singled out.”

Bratton reiterated his support for stop-and-frisk on Thursday but has likened it to chemotherapy, saying that it must be utilized in proper doses.

“We have a situation in this city at this time that is so unfortunate,” Bratton said. “At a time when police and community should be so much closer together, that there should be a bond of legitimacy and trust between them, it’s not the case in so many communities in this city. It’s unfortunate. But it can be corrected.”

To illustrate his commitment to improving relations with the community, Bratton displayed the children’s book “Your Police,” which he said he began checking out regularly from the Boston Public Library as a youth.

“I’ve taken this book everywhere I’ve ever gone, every department. It’s always proudly displayed, because it had such profound influence on me,” he said. “On the last page of this book, it reads, ‘We must always remember that whenever you see a policeman, he is your friend.'”

Bratton, known for his outsized personality and fondness for the limelight, was police commissioner under Rudy Giuliani, a Republican, from 1994 to 1996. Bratton emphasized the broken-windows theory of police work — that criminals who commit small crimes, such as vandalism, also commit more serious crimes.

Bratton also helped spearhead the use of CompStat, a data-driven system of tracking crimes that allows police to better allocate their resources to high-crime areas. The real-time system, which is still used today, “changed the game forever,” de Blasio said Thursday.

Crime immediately plummeted under Bratton, but he frequently fought with Giuliani over who deserved credit. He resigned after two years.

Bratton led the Boston Police Department and the formerly independent New York City Transit Police before running the NYPD. He has been working at private security firms since 2009 and was appointed by de Blasio almost 20 years to the day after he was first selected to run the department by Giuliani.

Kelly has been praised as one of the most effective commissioners in the NYPD’s history. Besides overseeing the historic reduction in crime, he dramatically bolstered the NYPD’s surveillance capabilities after the 2001 terror attacks. The NYPD says it has foiled terror plots but has come under criticism for its surveillance of Muslim communities, revealed in a series of Associated Press stories.

Bratton hasn’t commented on the surveillance program.

Last year, New York City reported 414 murders, a record low, and this year is on pace to be lower still.

(AP)