A day after Denver’s safety manager announced an investigation into Deputy Police Chief Matt Murray, the district attorney’s office confirmed it has opened a criminal investigation.

The DA’s office will investigate a possible criminal violation of the Colorado Open Records Act, which is also one focus of the city’s investigation into Murray.

Both investigations relate to Murray’s handling of an internal affairs investigation of a now-former officer who was accused of sexual assault.

Murray is in charge of the department’s administration division and serves as the chief of staff for Denver Police Chief Robert White.

The DA’s office released a statement to 9NEWS after receiving a request for an investigation from DPD’s main police union.

"Based upon a request made last week by the [Denver Police Protective Association] to one of the chief deputies in the office, Denver District Attorney Beth McCann has determined that communication to be a sufficient formal request to the District Attorney for a CORA violations investigation,” the statement read.

The city’s investigation was announced Thursday by safety manager Stephanie O’Malley. A third-party investigator will look at Murray’s actions in the case, O’Malley said in a statement. The case never resulted in criminal charges.

In an emailed statement, O’Malley said, “as Executive Director of Safety, it is my duty to provide civilian oversight to the Denver Police Department. As such, I have decided to initiate an outside, third-party investigation into this matter to ensure transparency and accountability.

The Office of the Independent Monitor will monitor the third party investigation, which will include the arrest associated with former Denver police officer Devin Munk's internal affairs case, and the subsequent handling of a related open records request."

On Thursday, Murray sent a statement to 9NEWS that read:

“Chief White and I welcome an independent third-party investigation into these allegations. This investigation will disclose the truth of this matter and will put it to rest. We have been very clear and transparent with the facts in this case.”

The investigation stems from 2016 incident in which then-Denver police officer Devin Munk and a woman named Angiella Arnot were arrested on suspicion of sexually assaulting another woman. Both were briefly jailed, but no criminal charges were ever filed. Munk later resigned from the department.

RELATED: No charges for DPD officer arrested for sex assault

Munk could not be reached for comment. Arnot has repeatedly declined requests for an interview from 9Wants to Know.

On May 17, 2016, then-Denver District Attorney Mitch Morrissey sent a letter to Chief White criticizing Murray’s involvement in the investigation.

The third party investigation of Murray partially stems from that letter.

“The information that exonerated Ms. Arnot was in the hands of DPD detectives from the beginning of the investigation,” reads Morrissey’s letter, which was obtained by 9Wants to Know. “The data needed only to be downloaded from the victim’s cell phone. Ms. Arnot did not present a danger to anyone, so conducting a more thorough investigation and reviewing the victim’s cell phone data should have preceded her arrest.”

In a June 3, 2016, letter obtained by 9Wants to Know, White acknowledged receiving Morrissey’s letter and said, “I will look at the totality of the situation and will ensure that the appropriate action is taken.”

In an interview with 9Wants to Know earlier this year, Murray said he did nothing wrong, adding DPD believes in the concept “start by believing,” when it comes to sex assault allegations and, as a result, the arrests were proper.

The Police Protective Association, the union that represents most police officers employed by DPD, researched the case. The PPA filed an open records requests with Murray’s office in December and January, asking for the copy of the Morrissey letter that was delivered to the chief.

According to the records obtained by 9Wants to Know, the PPA asked for any communication regarding the case between the DA’s office, DPD and Chief White.

In one of the email exchanges between the records administrator and Deputy Chief Murray, obtained by 9Wants to Know, Murray wrote, “I have no records responsive to this request.”

PPA President Nick Rogers told 9Wants to Know in a statement Thursday night, “regarding the investigation into Deputy Chief Murray, the PPA is very happy to learn that the Manager of Safety's office is finally taking this investigation seriously and is asking for an outside investigator to look into Chief White and Chief Murray’s actions, which I believe rise to the level of a criminal act for intentionally not releasing documents to the PPA under the Colorado Open

Records Act. They attempted to cover this story up and I am thankful that it is being brought to the attention of our citizens.”