(AP) -- Four senior New York City police officials have been transferred amid a corruption probe into whether officers took free trips, meals and other perks, and Commissioner William Bratton said Thursday police and federal investigators will "follow the leads wherever they take us."

"The public has an expectation of a high degree of trust and integrity in its police department," he said. "This is not a particularly good day for the department."

The corruption investigation by the NYPD's Internal Affairs Bureau began in 2013, Bratton said in a statement. In early 2014 the FBI and Department of Justice became involved in the inquiry. Bratton said the inquiry is focused on current and former officers as well as others. The potential issues include violations of NYPD rules and policy, city conflict of interest rules and federal criminal laws.

A law enforcement official told The Associated Press that federal investigators have questioned nearly two dozen officers in the probe on whether they took gifts from two politically connected businessmen and members of Brooklyn's Orthodox Jewish community in exchange for favors. The official didn't know the nature of the favors the police were suspected of trading. The official was not authorized to speak publicly and spoke on condition of anonymity.

No one has been charged criminally.

Bratton said Deputy Chief Michael Harrington and Deputy Inspector James Grant were stripped of their guns and badges and placed on desk duty and transferred from their posts as the executive officer of housing and commander of the 19th Precinct in Manhattan. Deputy Chief David Colon, commander of housing in Brooklyn, and Deputy Chief Eric Rodriguez, the No. 2 of the patrol borough Brooklyn south, were also transferred.

NYPD officers in the rank of captain and above will receive additional training regarding conflict of interest rules, police said.

"We don't believe based on what we know so far that this is deep systemic corruption throughout the department as opposed to pronounced bad judgment of a small group of people that are relatively senior, but we're going to go where the investigation and the facts take us," said Lawrence Byrne, deputy commissioner for legal matters.

Roy Richter, head of the Captains Endowment Association which includes all high ranking members, defended the officers and called the personnel moves "traumatic."

"I do not know of any police commanders to be the subject of an FBI probe and hope the federal investigation is wrapped up quickly to allow them all to defend their reputations in an open forum," he said.