Former Liberal minister Alan Tudge has denied he was responsible for checking whether or not the robodebt scheme was legal.
Mr Tudge, who was human services minister between 2016 and 2017, told the royal commission into the Centrelink debt recovery scheme that while he was in charge of department matters, it was not his responsibility to ascertain whether the program was legal.
However, he said he was responsible for robodebt's "lawful implementation".
During his appearance at the commission on Wednesday, Mr Tudge said while he did not consider the legality of the robodebt scheme, questions were raised about the program's fairness.
"It is unfathomable for a (department) secretary to be implementing a program which he or she would know to be unlawful. It is unfathomable," he said.
The scheme, which used averaging on incomes to determine debt levels, ran from 2015 to 2019, continuing to operate despite concerns over its legality.
The controversial program recovered more than $750 million from more than 380,000 people.
Several people took their own lives while being pursued for false debts.
The former minister said he had no recollection of being "excited" about the prospect of recovering money as part of data-matching activities, despite emails between tax office staff presented to the commission stating he was.
Mr Tudge told the commission he could not remember looking to extend the time period officials could use to recover debts.
Concerns were raised that the time period could have been stretched back to as far as 2000.
Not long after Mr Tudge became human services minister, then finance minister Mathias Cormann asked if there was any way to find more budget savings in the portfolio, the commission was told.
While concerns about the legalities of robodebt were raised by the media in late 2016 and early 2017, Mr Tudge said he was focused on the scheme's implementation.
On Tuesday, the royal commission was told Mr Tudge sought the Centrelink file details of robodebt recipients who spoke out about the scheme in the media.
Former Liberal minister Christian Porter, who was in charge of social services during the scheme's operation, will appear before the royal commission later this week.
