“There are delays that will occur in good faith and then the department will be accused unfairly of sitting on data,” Mr. Browne said, citing the difficulties and cost for an organization designed to fight crime to quickly produce statistics. But, he added, “The reality is there’s troves of information and data being provided like never before.”

Mr. Browne’s departure comes at a transitional moment for a Police Department facing twin challenges in an election year: two City Council bills that would increase oversight of the department are likely to be vetoed soon, and a federal judge is preparing to render a decision in the coming weeks over its stop-and-frisk practices.

For roughly two decades, Mr. Browne and Mr. Kelly have faced such challenges together, said colleagues and longtime police reporters. “He’s my consigliere,” Mr. Kelly playfully said of Mr. Browne in a 2001 interview in The New York Times, using a reference to “The Godfather” film.

“We’ve been involved in a lot of experiences, some of them hairy,” he said in the interview, referring to their work in Haiti, where Mr. Kelly was director of the International Police Monitors starting in 1994, and Mr. Browne was his deputy.

Patrice O’Shaughnessy, a former reporter for The Daily News who covered the police for two decades and reported on the two men’s work in Haiti, said that they “just get along very well, similar backgrounds, Irish Catholic.” That was apparent, she said, when Mr. Browne began working with the press under Mr. Kelly the first time he was commissioner in the early 1990s, as well as during his current tenure. (Mr. Browne became the top spokesman in January 2004.)

“Kelly brought him in because he was a former reporter,” she said. “He knew what we were looking for.” But, Ms. O’Shaughnessy added, reporters’ access grew more limited after the Sept. 11 attacks.

“It was a different atmosphere,” she said, comparing recent years with past decades when precinct commanders were more available to speak directly with reporters. “They became much more restrictive in terms of information,” she said.