DENVER (CBS4)– CBS4 has learned that an internal investigation is underway into the interim head of the Denver Sheriff Department, Elias Diggins, and the captain in charge of the Denver Sheriff’s Internal Affairs Bureau after an internal affairs investigator blew the whistle, saying he was ordered to destroy a videotape that showed an inmate being humiliated and degraded.

“This is the definition of corruption,” said Brent Miller, who believes the sheriffs department fired him earlier this month for refusing to destroy the tape. Miller worked for the Adams County Sheriff’s Office for nearly 26 years before retiring. He then agreed to go to work for the Denver Sheriff Department as a civilian internal affairs investigator, brought on to help clear up a backlog of internal affairs cases.

“It was a huge challenge. I loved it and looked forward to going to work every day,” said Miller.

Miller said he was assigned to investigate several complaints filed by jail inmate Christopher Colbruno. Earlier this month, he was assigned yet another case involving Colbruno. Sheriff’s deputies were transporting Colbruno to Denver Health Medical Center for medical attention, but at some point Colbruno defecated on himself and his jail clothing. Before entering the hospital , deputies removed Colbruno’s clothing and walked him through hospital hallways wearing only handcuffs, but no clothing.

Personnel at Denver Health Medical Center felt the inmate had been subjected to inhumane and degrading treatment by being forced to walk nude through the hospital hallways so they filed a complaint with the Denver Sheriff Department. The complaint was assigned to Miller. On May 11, Miller and a second investigator traveled to Denver Health Medical Center to obtain a copy of hospital videotape showing Colbruno in the hospital.

When he returned to his office with the tape, Miller said he was approached by Captain Paul Ortega, who leads the Sheriff Department’s internal affairs bureau.

“He asked me if I had uploaded this video yet and I told him I had not and told me,’good, don’t do that because they’re making that go away, it’s not going to be a case anymore.’”

CBS4 asked Miller a second time to recount what he was told by Capt. Ortega, “He told me don’t upload it they’re making it go away. Who is they? He said the sheriff then told me to get rid of the video. Do not upload it get rid of the video and I immediately told him that’s not ethical to get rid of evidence in a case.”

Miller said Captain Ortega agreed with him but said, “That’s the way it is.”

Miller said he refused to destroy the tape and instead gave it to another investigator for safekeeping.

The next day, May 12, Miller was told to report to Ortega’s office.

“I was told I was being terminated by the Denver Sheriff Department because I was too opinionated and they wanted to go in a different direction,” said Miller.

The termination order obtained by CBS4 was signed by Sheriff Elias Diggins, who Ortega said had told him to have the tape destroyed.

Contacted by CBS4, Diggins declined to discuss the CBS4 report, “I cannot talk about any internal investigation.”

Captain Ortega did not respond to multiple inquiries from CBS4.

“I believe I was fired because I stood up to what I perceived to be unethical behavior and corruption by the Denver Sheriff’s Department and the Manager of Safety’s Office,” said Miller. “I expressed those opinions that what they were doing was unethical, improper and corrupt and I didn’t want to be a part of it. I cannot be part of losing evidence or getting rid of evidence or letting those collusions of corruption go on within the city. I don’t want to be a part of that.”

After CBS4 began making inquiries, Stephanie O’Malley, Denver Executive Director of Safety released this statement: “I have directed the Internal Affairs Bureau of the Denver Police Department to investigate allegations of misconduct by command officers in the Denver Sheriff Department,” wrote O’Malley. “This investigation was initiated immediately after I learned of the allegations and their nature.”

She declined to address specifics of the CBS4 Investigation but wrote that, “I am able to verify that Senior Investigator Miller did not pass his employment probation with the City of Denver due to performance issues unrelated to the allegations referenced above.”

Miller disputes that assessment saying he was always told his work was solid and there were no issues.

Miller has now hired an attorney who plans to file a federal lawsuit against the Denver Sheriff Department saying Miller was fired as retaliation for exercising his first amendment rights.

“We do believe there is evidence to corroborate what happened here,” said attorney Donald Sisson. “We think there is ample evidence that will prove Brent Miller’s case.”

Sisson said in his view, it’s no coincidence that Miller refused to destroy a videotape then was told the next day that he was being fired.

“I want the people to really know what’s going on,” Miller told CBS4. “I just want things to be honest and fair and that’s the way Denver needs to do business.”

The provocative revelations from Miller come a week after an independent consultant released an extensive report recommending sweeping changes at the Denver Sheriff Department.

CBS4 Investigator Brian Maass has been with the station more than 30 years uncovering waste, fraud and corruption. Follow him on Twitter @Briancbs4.