An outside agency should look into allegations by a former Denver Sheriff Department internal affairs investigator that he was ordered to destroy or withhold evidence, the sheriff’s deputies’ union said Tuesday.

Stephanie O’Malley, executive director of the Department of Public Safety, cannot conduct an impartial investigation, according to the Denver Sheriff Lodge #27 and the Colorado Fraternal Order of Police.

O’Malley asked the Denver Police Department’s internal affairs bureau to investigate the allegations leveled by Brent Miller, who was fired in May after six months on the job.

“As the Safety Director for Denver, she is in authority over the Denver Police as well as the Denver Sheriff Department, so it doesn’t seem possible that the Denver Police can be unbiased as they investigate a matter that may involve an improper decision by Stephanie O’Malley or members of her office,” the news release said.

Miller last week filed a whistle-blower lawsuit against O’Malley, Sheriff Elias Diggins, a deputy safety manager and two captains.

Officials in the safety department influence internal investigations to protect favored deputies while undermining those they do not like, the lawsuit claims.

Miller said he was told to get rid of video footage that showed deputies escorting a handcuffed, naked inmate through Denver Health medical center. His supervisors allegedly said that order came from Diggins, the lawsuit says.

Denver Health employees had filed complaints against deputies who escorted the naked inmate through the hospital’s halls.

Miller also alleged that he was ordered to delete information from an investigative report that would have exonerated a deputy who was involved in an arrest while working off-duty security at a restaurant.