Bill Bratton took over the reins of the largest municipal police force in America on Thursday, presenting himself in his new role as commissioner of the New York police department as a “change agent” who would tackle his predecessor’s widely denounced stop-and-frisk tactics.

Confirming his reputation as an assertive leader who does not shirk a fight, Bratton, 66, waded straight into the stop-and-frisk controversy as he was unveiled at a ceremony at the NYPD’s headquarters in One Police Plaza. He said the controversial policy that rose steadily under the previous commissioner Ray Kelly and focused on black and other minority communities in the outer boroughs had been “objected to by so many in this city”.

He added that “many in this department felt there was something wrong, it was just not happening the way it should have. I think we can find the right amount where we have a safe city, and communities and police that respect each other.”

Bratton’s outspoken criticism of a centrepiece of policing strategy in New York over the past few years echoed a central campaign pledge of his boss: the newly enshrined mayor of the city, Bill De Blasio. The Democratic politician made putting an end to stop-and-frisk at the centre of his bid for the mayoralty.

In his remarks, De Blasio thanked Kelly for having served the city with “extraordinary distinction and integrity”. But he went on to repeat his emphasis on the need for change, calling Bratton a “progressive crime-fighter who recognises that the streets will be safer, and crime will be reduced even further, when police and community work together. Safe streets and respect for individual liberty go hand-in-hand.”

Bratton has now begun his second stint as head of the 35,000-strong NYPD, following a three-year term in the 1990s under then mayor Rudy Giuliani and a later term at the helm of the Los Angeles police department. He was forced out of the New York job in 1996, reportedly because Giuliani resented his media-savvy police commissioner hogging the limelight.

“Who says you can’t come home again?” Bratton quipped at his inauguration. “And this is home. It is great to be back.”

Paradoxically, Bratton’s first stint as NYPD chief in the 1990s is seen as the start of the aggressive police tactics that helped turn around the city’s terrible crime statistics but also spawned stop-and-frisk in the first place. During his 27 months in the commissioner’s job, he pioneered the “no broken windows theory” that focused on minor infractions in order to create a culture in which serious criminality could no longer flourish.

The approach was continued, and deepened, under Kelly, with the murder rate falling from its 1990 peak of 2,245 to a record low of just 333 last year.

Bratton’s comments made clear that he is aware of the sensitive tightrope he now has to walk in a city as he takes over policing in a city with such an extreme history, from the near-anarchy of the 1970s and 80s to today’s relative tranquility. On the one hand, he has to implement De Blasio’s campaign promises on stop-and-frisk, but on the other he is aware that he cannot afford any uptick in crime statistics or any appearance of weakness in combatting the threat of terrorism in the wake of 9/11.

“I understand the shoes I am stepping into,” Bratton said, referring to the historically-low crime figures achieved under Kelly.

But he went on: “It is unfortunate that even as this dept can celebrate its tremendous record at reducing crime to historic lows, removing the chaos and disorder this city exemplified in the 1980s, we have not achieved the collaboration that all that success should have brought about.”

He said there was a “mystery” to solve – that when “so much positive has been done, where did we disconnect? The challenge for all of us is to find that disconnection and heal it. That’s why I came back.”