The issue focused on a series of incidents involving officers at the agency's Phoenix police headquarters.

The Phoenix Police Department has hired a former federal prosecutor to investigate complaints from two former colleagues. The investigation, which began last week, has focused on the conduct of Phoenix police officers who worked there, officials said.

The investigation comes after the city of Phoenix, which oversees the Phoenix police department, agreed to pay $9.5 million to settle allegations it violated the Constitution and federal civil rights laws during the investigation