Metadata unlawfully obtained by ACT Policing in 2015 was involved in one conviction, but the ACT Director of Public Prosecutions said he was satisfied the evidence was never relied on and that no prosecutions were affected.
The director, Shane Drumgold, said the metadata involved in the ACT Supreme Court criminal prosecution could have placed a person at a particular place at a particular time.
But he said while the information was in the periphery of the brief of evidence, it was never considered, never led in court and was never in evidence.
He told The Canberra Times that the illegally obtained metadata was not necessary in the prosecution, because there were also eyewitnesses who had placed the person at the relevant place.
"I'm satisfied that no prosecutions were impacted, I'm satisfied the evidence was never used," he said.
Mr Drumgold said he had been briefed on the case on Friday evening but for privacy reasons he could not identify the case, nor would it be appropriate to reveal the charge.
He said it was a serious criminal prosecution in the ACT Supreme Court that had resolved with a guilty plea.
Of a second criminal investigation flagged by ACT Policing as potentially affected, Mr Drumgold said the case never went to a prosecution and so the metadata never came to his office.
Mr Drumgold said all investigating agencies needed to be vigilant and ensure they have the right supporting data and the right supporting application processes.
"That's absolutely essential to the admissibility of this evidence," Mr Drumgold said.
"If the supporting material isn't there we won't attempt to lead evidence of this nature, so if all of the appropriate delegations are not in place the evidence is not legally obtained."
If proper procedure had not been followed, Mr Drumgold said that should be disclosed at the earliest possible opportunity so that prosecutors can make decisions.
Mr Drumgold noted there were exceptions in evidence law that allowed unlawfully obtained evidence to be admitted into evidence in certain circumstances.
Last week, ACT Policing, a branch of the Australian Federal Police, admitted it unlawfully accessed people's metadata a total of 3,365 times, not 116 as had been disclosed in an explosive commonwealth ombudsman's report earlier last week.
An "administrative oversight" in March 2015 led to the relevant position being "inadvertently omitted from the list" of people authorised to approve metadata searches.
"The ACT Policing position holder, who previously held the appropriate delegation, had continued issuing authorities in good faith unaware that the delegation had been omitted," a statement from ACT Policing read.
The issue affected 116 cases in October 2015 and was disclosed to the ombudsman in that month.
But it was not until 2018 that another 3,249 cases were uncovered going back to March that year.
Steven Whybrow, president of the ACT Bar Association, said without full transparency and accountability there was no incentive for the police not to do it again.
"As the fallout of the Lawyer X scandal continues to identify miscarriages of justice, there needs to be transparency about what the police did in relation to specific cases so its impact can be properly assessed," he said.