IOWA CITY — In a move the Iowa City manager concedes is unusual, a police captain voluntarily has demoted himself two ranks, to sergeant.Iowa City Police Chief Sam Hargadine confirmed Monday that Doug Hart, formerly the captain of administrative services for the police department, has been voluntarily demoted to sergeant of training and accreditation.Hart could not be reached for comment Monday and neither Hargadine nor City Manager Tom Markus disclosed the reasoning behind the personnel change.“I’m not going to make any comments on that because we’re getting into the personnel side,” Hargadine said.Hargadine said the decision did not involve any illegal activity nor did it involve anything that put public safety or the department’s integrity at risk.