(CNN) -- John Miller, who has moved back and forth between public service and journalism like few others in either profession, is doing it again.
This time he's leaving CBS News, where he has been a senior correspondent for two years, and joining the New York Police Department.
Miller announced his latest move on Thursday. He embodies something that is, for some media critics, a source of great concern: the so-called "revolving door" between the people who cover the news and the people who are being covered. For CBS, he's something else: a fount of great knowledge who will be almost impossible to replace.
David Rhodes, the president of the network news division, said Miller's decision was "a loss for CBS."
"He's been really great for us," Rhodes said in a telephone interview on Thursday.
CBS allowed Miller out of his contract with the network because, as Rhodes put it, "it would just be inappropriate to stand in the way" of a return to public service. Miller's exact title at the NYPD is not yet known. But he'll have a high-profile job in counterterrorism, reuniting with his former boss William Bratton, who was the commissioner of the police department in the mid-1990s and will return to that position in January.
Miller worked for local television stations in New York before going to work for Bratton as a spokesman for the NYPD in 1994. He subsequently worked for ABC News; the Los Angeles Police Department, again under Bratton, who had become police chief there; the FBI; and the office of the Director of National Intelligence. In late 2011 he joined CBS as a senior correspondent. When asked at the time about Miller's moves back and forth between journalism and law enforcement, Rhodes said, "He understands journalistic sources and methods and he understands our values."
On Thursday, Rhodes said of the revolving-door situation and Miller, "He's traveled through it a number of times," and added "we don't think it's a bad thing."
Rhodes praised Miller for having an unmatched Rolodex of sources and said CBS has "benefited from that greatly." Among the stories Rhodes cited were the mass shootings in Aurora, Colorado, and Newtown, Connecticut, when Miller was frequently on television to share information he had obtained from law enforcement sources. Rhodes added, "John was the reason why we didn't go with the erroneous reports of an arrest in the Boston bombings." (A number of other news organizations, including CNN, prematurely reported an arrest had been made two days after the April explosions.)
"There's nobody like him, and I think people around the television industry would agree with that," Rhodes said. "They all would have liked to have him on those, and many more stories that he's done for us."
Miller's close relationships with law enforcement sources, however, are among the reasons why some media critics have objected to his role at CBS and his repeated transitions from public service to journalism.
They say the revolving door creates conflicts of interest for Miller and reporters like him. Miller's "60 Minutes" report about the National Security Agency met with disapproval by media critics earlier this month in part because of his pending move to the NYPD.
(Michael Calderone of The Huffington Post said on CNN's "Reliable Sources," "John Miller has left journalism twice before." Calderone listed Miller's prior jobs and said that in the "60 Minutes" report, "He disclosed only one of those for law enforcement roles.")
Rhodes indicated that he didn't think the report on the NSA was a conflict of interest.
He said on Thursday, "If he (Miller) was covering the NYPD, that would have been inappropriate."
Miller's move was announced via a news report on WCBS, the CBS affiliate in New York City. In an interview, Miller alluded to the fact that he'll be involved in the city's counterterrorism efforts, saying of New York, "They have certainly the biggest, most complex and forward-leaning counterterrorism operation of any police department in the world, so it will be a great challenge that I hope to rise to."
Rhodes said CBS News would seek to replace Miller soon, possibly through a combination of new hires.
"If and when he decides to return to journalism, we'd welcome him back," he said.