William Bratton, the police commissioner who led departments in Boston, Los Angeles and New York and saw his crime fighting strategies copied across the nation, will end his unparalleled law enforcement career with a ceremonial send-off Friday in the city that was the setting of his biggest triumph.

Bratton, 68, is due to participate in a traditional “walkout” at New York Police Department headquarters, where commanders line up in formation to bid him farewell as he leaves three years into his second stint as the city’s police commissioner.

His goodbye is well timed. Violent crime in New York City remains near a modern-day low. Yet, debate is likely to continue indefinitely over how much credit Bratton should get for New York’s transformation from the bloody mess it was in the 1980s and early 1990s.

Friday’s ceremony comes just a week after Bratton fiercely defended the legitimacy of his signature “broken windows” strategy — an idea, first proposed by social scientists James Wilson and George Kelling, that you can deter violent crime by cracking down on lesser types of lawlessness, like graffiti or turnstile jumping.

Bratton earned wide acclaim for his assaults on so-called “quality of life” crimes, and for mining crime data to deploy his forces more effectively.

New York City’s homicide rate had already begun to drop in the two years before he became commissioner in 1994, but during his 27-month tenure it plummeted. Between 1993 and 1995 killings fell by 40 percent, erasing two decades of climbing murder rates.

Homicides fell another 35 percent in the two years after Bratton left the department, forced out by Mayor Rudolph Giuliani.

In more recent years, though, some criminologists have concluded that the impact of broken windows on violent crime is minimal.

In March, the independent inspector general for the New York Police Department issued a report concluding that focusing on offenses like urinating in public and riding bikes on sidewalks had no influence on felony crime rates.

It also accused the 36,000-officer department, the nation’s largest, of unfairly singling out communities of color for quality-of-life enforcement at a time when Mayor Bill de Blasio has emphasized protecting civil rights.

Bratton pushed back last week with characteristic aplomb, saying the report was the work of “amateurs” and had “no value at all.”

There is no consensus today about what caused New York City’s turnaround in the 1990s, or what caused similar, dramatic improvements in violent crime rates in many other U.S. cities at the same time.

“The idea that the NYPD has a huge impact on crime was always a very dubious claim,” said Eugene O’Donnell, professor of police studies at John Jay College of Criminal Justice.

After leaving New York the first time, Bratton worked in the private sector, then took over a scandal-scarred Los Angeles Police Department in 2002.

There, he presided over both a decline in violent crime and an easing of some tensions between the department and black and Hispanic communities. Bratton left Los Angeles in 2009 with high approval ratings.

After returning to lead the NYPD again in 2014, Bratton saw perhaps the biggest crisis of his tenure: the death of an unarmed black man, Eric Garner, at the hands of a white police officer trying to arrest him for the minor crime of selling loose cigarettes.

The death sparked angry protests.

It also fueled a backlash in some quarters against “broken windows” enforcement.

That outcry, though, hasn’t caused city leaders to back away from the tactics, or the man, often credited with leading New York out of the darkness.

“The same strategy that helped make us the safest big city in America,” Mayor de Blasio said recently, “is still making us the safest big city in America.”

(AP)