MIAMI BLUE.

On a sunny morning last fall, John Timoney, the Miami chief of police, changed into navy-blue shorts and a short-sleeved shirt with "POLICE" stencilled on the back and wheeled his mountain bike out into the parking lot of the department's headquarters, where about two dozen of his top officers were waiting. For more than four hours, Timoney led them on a twenty-four-mile tour of Miami, looping through the predominantly African-American neighborhood of Overtown, then north to the Korean-dominated Fashion District, and through the Design District and Little Haiti. After a break for lunch, Timoney picked up the pace and led the group south along Biscayne Boulevard, across the Flagler Street Bridge, and into Little Havana. There was a triumphal feel to the ride, which Timoney leads at least twice a month.

Timoney, who is fifty-eight, has short reddish-gray hair and the ruddy face of an Irish boxer. He is just under six feet tall. When he walks, he bounces on his toes with his chest puffed out, "like James Cagney in 'Yankee Doodle Dandy,' " as William Bratton, the former New York City police commissioner, noted in his 1998 memoir, "Turnaround." Timoney is widely regarded today as one of the most progressive and effective police chiefs in the country--a reformer and an iconoclast. In New York, where he served under Bratton, Timoney talked about replacing steel handcuffs with Velcro straps--pink if possible. In Philadelphia, where he was police commissioner for four years, he had his force trade in their blackjacks for pepper spray, and he gave women's groups the right to review sex-crime cases. Timoney speaks in what a friend calls a Bronx brogue, an accent that evolved from a childhood spent in Dublin and Washington Heights. (When Timoney was twelve, the family moved from Ireland to New York to join his father, who had found work as a doorman on Fifth Avenue.) He can be abrupt and defensive when dealing with critics--reporters have found him to be exceptionally thin-skinned--and he has got into trouble for his occasional outbursts, perhaps most memorably during a blowup at Rudolph Giuliani when he was mayor of New York. "I've always sold big. Very controversial. Big mouth. Loudmouth," he says, as if he didn't much care.

When Timoney took the top police job in Miami, in January, 2003, he inherited a department that had major prob-lems, not the least of which was an alarming record for shooting civilians. The Miami Herald, in a series in November, 2002, called that record "an escalating pattern of reckless shooting"; Raul Martinez, the chief of police, resigned in 2002, and the mayor, Manny Diaz, asked the Department of Justice to investigate. On the day that Timoney was sworn in, eleven Miami cops went on trial in federal court on charges of conspiring to plant guns on unarmed suspects in order to cover up police shootings.

In the decade before Timoney's appointment, Miami police had killed twenty-eight people and fired at another hundred and twenty-four. During his first twenty months on the job, no Miami cop fired a shot, a phenomenon that appears to be unique in a city of Miami's size. In the four years of his tenure, police have shot at seven people, killing two and wounding four. The murder rate in Miami has dropped from about twenty to fourteen per hundred thousand in the years since 2003. (Although major crime over all dropped in 2006, there was an increase in the number of killings in Miami.) Credit for the drop certainly does not belong solely to Timoney; there has been a nationwide renaissance in police work and in attitudes toward policing, and crime in many American cities, including Miami, fell steadily during the nineteen-nineties. In New York, where much of this change was pioneered, Timoney held several top jobs with the N.Y.P.D.

Timoney joined the N.Y.P.D. in 1967, at the age of nineteen. He quickly made his name at the Forty-fourth Precinct, on Sedgwick Avenue in the Bronx, where he had a top record for arrests. He also earned a B.A. in American history from John Jay College and went on to get master's degrees in both American history and urban planning. In the early eighties, he was placed in charge of reviewing firearm use and became deeply interested in reforms, announced in 1972, that restricted how and when police could use their weapons. What he discovered was that, in the year before the restrictions were imposed, New York police fired their weapons about eight hundred times, and some ninety people were killed; dozens more were wounded. About a dozen officers were killed.

The pattern changed dramatically after August, 1972, when the prohibition was announced: according to Timoney, shootings in the last third of that year dropped by ...