Denver Police Chief Robert White may have violated his department’s policies for handling complaints — and perhaps a city ordinance — after the district attorney last year questioned how the chief’s second-in-command ran an investigation, a Denver Post review of the policies has found.

Already, the city has launched an independent investigation and a criminal probe into the actions of Deputy Chief Matt Murray. But the situation also raises questions about who in the police department’s administration knew about a May 17 letter written by then-District Attorney Mitch Morrissey that expressed concerns about Murray’s actions and how those people responded once the letter came to their attention.

If the independent investigation expands into whether police department policies and a city ordinance were violated, it could hinge on simple questions: Should the district attorney be considered a citizen? And what qualifies as “serious misconduct” under the department’s operations manual?

The Denver Police Protective Association, which represents rank-and-file officers in disciplinary cases, said White’s failure to immediately open an internal investigation represents a double-standard when it comes to disciplinary procedures.

“I guarantee if the district attorney had written a letter about any other officer, it would have been sent to internal affairs and a case would have been opened immediately,” said Bryan O’Neill, the PPA’s vice president. “For years, this chief and deputy chief have pushed transparency and accountability — their two favorite words — on everybody in the department. This is a clear example that they’re not adhering to their own principles.”

Stephanie O’Malley, the Department of Safety’s executive director, has hired Flynn Investigations Group, a Denver law firm, to conduct an independent investigation into Murray’s actions. Denver District Attorney Beth McCann also has opened a related criminal investigation into whether Murray may have violated the state’s open records laws.

O’Malley has not said when she learned of Morrissey’s letter. She announced the third-party investigation on March 2.

Daelene Mix, spokeswoman for the safety department, declined to comment on behalf of O’Malley and White, saying, “Until this matter is resolved, it would be inappropriate to discuss details associated with the pending investigation.”

Mayor Michael Hancock’s office said the third-party investigation is an appropriate step toward getting to the bottom of what kind of action the chief and safety director should have taken when they first received Morrissey’s letter.

“We will look to the outcome of that investigation to determine if there was any misconduct or missteps,” mayor spokeswoman Jenna Espinoza said in a statement.

The episode began with Morrissey’s letter in May to White in which he expressed concerns about Murray’s direction of an internal affairs investigation into a police officer and a female accomplice. They were accused of sexually assaulting another woman. The charges later were dropped, but police issued news releases about their arrests, and Morrissey said Murray’s decision-making tarnished the reputation of the accused woman.

In the letter, Morrissey said Murray disregarded a long-standing policy that instructs officers to consult with an on-call deputy district attorney for guidance when conducting investigations. If Murray had followed that protocol, charges likely would not have been filed against the woman, Morrissey said. The letter also said Murray had a “cavalier attitude” when confronted about his actions.

Morrissey called his letter unprecedented in his 12 years as district attorney and said he had thought White was going to open an internal review. The chief had told Morrissey in a two-sentence letter on June 3 that he would “look at the totality of the situation and will ensure appropriate action is taken.”

“I figured that was going to happen,” Morrissey said.

But no internal investigation was opened, Murray told The Post in an interview before the third-party investigation was ordered.

“There’s no need,” Murray said. “An investigation is to determine the facts, and the chief already knew the facts. He didn’t need an investigation to tell him what he already knew. He was in the best position to know the facts.”

The police department’s operations manual, which sets standards for all officers to follow, says supervisors must notify the internal affairs division of allegations of general misconduct. But the manual has provisions for the chief to dismiss complaints, including when no misconduct exists or when the complaint is deemed frivolous.

The manual also says the “(Internal Affairs) commander, the Chief of Police or the Executive Director of Safety will report all allegations of serious misconduct, including conduct prohibited by law, to the Office of the Independent monitor within three business days of becoming aware of the allegations.”

But Monitor Nick Mitchell told The Post he did not know about the letter until Jan. 30 — eight months later — when KMGH-Channel 7 aired a report about Morrissey’s letter.

“When that first story ran, that’s when I became aware of the letter,” Mitchell said.

Mitchell said he was not able to further discuss the letter and related protocols because of the ongoing investigation into Morrissey’s complaint and how it was handled.

Denver’s municipal code, which establishes parameters of the Office of Independent Monitor, requires police to notify the monitor within three business days of receiving a “citizen complaint” about an officer.

Morrissey said Tuesday that although he was an elected official when he wrote the letter, he also is a citizen. And he certainly considered his letter a complaint.

“I would think to be safe, reading that ordinance, I would go ahead and notify all of those people,” Morrissey said. “Are you going to split hairs or are you going to notify those folks? If it was a gray area, we always erred on the side of what the law told us to do.”

The police union said Morrissey’s letter qualifies as a serious allegation, and an investigation should have been opened immediately.

“They should have followed their own protocols and have been transparent about what occurred,” said Nick Rogers, the Denver Police Protective Association’s president. “Obviously, there was no investigation until the letter appeared.”