EXCLUSIVE: The NT Ombudsman has dropped an investigation into allegations senior NT Police detective Wayne Newell perverted the course of justice while in a key role in the Zach Rolfe murder investigation, citing in internal documents that it is “not in the public interest” to pursue, the NT Independent can reveal.

The NT Police brass had caused confusion about the appropriate body to investigate the complaint against Sgt Newell after first referring the matter to the ICAC, who the NT Independent revealed last week had sent the complaint made by Zach Rolfe’s lawyers back to police.

It is understood the complaint was at some point also referred by the police brass to the Ombudsman to investigate.

But in a letter last week, Ombudsman Peter Shoyer told police he would not be investigating the complaint and that the matter was “not in the public interest”.

NT Police have made no official comment on the latest determination, and refused to answer questions, but it is understood to have caused anger within senior executive ranks with one senior member expected to resign within weeks, said to be in relation to the perceived lack of action on the serious allegations.

Mr Rolfe’s lawyer Luke Officer filed the complaint with Acting Commissioner Michael Murphy in June, accusing Sgt Newell of perverting the course of justice by allegedly interfering in the evidence of an expert witness in the Rolfe murder case and withholding evidence that was favourable to Mr Rolfe’s defence.

Asked why a corruption complaint into potentially the highest levels of the NT Police was not in the public interest to investigate, Mr Shoyer had a spokesman respond to the NT Independent’s questions, appearing to distance himself from the decision of the Office of the Ombudsman not to investigate the complaint.

“A decision that an Ombudsman investigation would not be in the public interest is not a decision that investigation by any entity for any purpose would be contrary to the public interest,” Ombudsman spokesman Brendan Schultz said in an email.

“Decisions on pursuit of Ombudsman investigations take into account a range of factors, which may include the age of the matter complained of, the nature of the allegations involved, any statutory limitations on who can make a complaint or what actions can be investigated, available resources and other forums for investigation.”

It is understood part of the refusal to investigate stems from an assertion by police that the complaint, filed in May, was more than 12 months out from the time of the alleged offences occurring.

However, the NT Independent has seen documents filed with police in May 2022 – two months after Mr Rolfe was found not guilty by a Supreme Court jury of the murder of Kumanjayi Walker – with allegations of perverting the course of justice remaining unaddressed.

The latest complaint, filed in June – seven weeks after former commissioner Jamie Chalker “retired” from the role – alleged that Sgt Newell may have engaged in “criminal conduct, such as, for example, perverting the course of justice”.

It also called for Acting Police Commissioner Michael Murphy to initiate an independent investigation into the matter or refer it to another body for investigation.

The criminal complaint included excerpts of court transcripts from the murder trial, as well as emails and other internal police material including the Pollock/Proctor coronial reports, that Mr Officer said was evidence that Sgt Newell withheld crucial evidence from the defence team and at other times manipulated expert evidence from a use-of-force expert that was used to secure the murder trial against Mr Rolfe.

“The Ombudsman dropping the investigation isn’t about protecting Newell,” a source familiar with the matter told the NT Independent.

“This is about protecting the senior executive and those who have been promoted after the Rolfe investigation.”

The confusion around which body will investigate the allegations of major misconduct in the NT Police is reminiscent of the confusion surrounding former commissioner John McRoberts’ forced resignation over allegations of perverting the course of justice in 2015.

Several bodies, including the Office of the Ombudsman and others eventually completed smaller, non-publicised reports into that matter that were not released publicly.

The Australian Federal Police were ultimately brought in to investigate independently of the NT Police.

Mr Murphy refused to say on Friday if he or any other member of the executive referred the criminal complaint against Sgt Newell to the AFP to investigate.

“This is not a matter for the AFP,” the AFP media unit responded on Friday evening after being asked if they were referred the matter or would investigate it.