It remains unclear how much the city will pay a retired judge to investigate “circumstances” that led Police Chief Frank Straub to place his assistant chief on paid administrative leave.

Assistant Police Chief Scott Stephens was placed on leave by Straub in December. City officials have declined to say what led to the action, saying it’s a personnel issue that can’t yet be discussed publicly. Stephens’ attorney, Bob Dunn, said this week that Straub placed Stephens on leave after he was accused of threatening work place violence in a private conversation with a friend who works within the department after Stephens had been told that he would be demoted.

Mayor David Condon announced on Monday that retired U.S. District Court Judge Michael Hogan, of Oregon, would perform the city’s Internal Affairs investigation into Stephens instead of city employees.

Hogan started work on the investigation this week, but there is not yet a final agreement on how much Hogan will be paid, said city spokesman Brian Coddington. He is expected to work on the investigation for about a month.