It has blamed "human error" for what the ACT Opposition has labelled "a serious blunder".

The Canberra Times on Tuesday revealed the self-described Alexander Maconochie Centre "ping pong champion", Cody Damien Herceg, had mistakenly been set free last week.

The situation came to light in the ACT Magistrates Court on Monday afternoon, when the 26-year-old appeared over the phone for a brief mention of four outstanding charges.

These included allegations of fraud and unlawful possession of stolen property.

His lawyer, Bowan Shelton, said it seemed jail staff had let Herceg walk away upon the expiry of a sentence for unrelated matters.

Court records indicated, however, that Herceg had been refused bail on the ongoing charges, which also include driving offences.

Magistrate James Lawton told Herceg to hand himself in "as soon as possible".

Herceg said he would "try" to do this, but the 26-year-old remains at large.

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On Tuesday afternoon, a Justice and Community Safety Directorate spokeswoman said it was common for prisoners to be simultaneously serving a sentence and on remand.

She told The Canberra Times information about Alexander Maconochie Centre inmates was kept on an electronic database, "which contains many files".

"Current release processes require manual checks across each of these files," the spokeswoman said.

"Due to human error, information in relation to the detainee being on remand was missed while assessing his release.

"The release of this detainee was an unfortunate error, and a review of this incident is being taken."

Questions were also put to Corrections Minister Mick Gentleman, who left it to the directorate to comment on behalf of the government.

The Canberra Liberals' corrections spokeswoman, Elizabeth Kikkert, had earlier said the ACT government should "absolutely" conduct an investigation into how Herceg was released.

"The cause of this serious blunder needs to be identified and rectified as a matter of urgency," she said.

Ms Kikkert said there were "certainly deficiencies" in release processes at the ACT's only adult jail, saying the territory government had not clearly set out the relevant policies.

"As a result, a detainee has casually walked out of prison on a date not set by the court," she told The Canberra Times.

"It wouldn't surprise me to see that lack of clarity in related policies contributed to this blunder."

The Opposition MLA described the incident as "greatly concerning", saying it was "certainly within the realm of possibility" that a violent inmate might also be erroneously released and the community placed at risk.

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