A National Anti-Corruption Commission inquiry on Wednesday found two of six people referred to it for investigation engaged in corrupt conduct, while it cleared the remaining four.
Those cleared included former Liberal prime minister Scott Morrison, who initiated the scheme while social services minister.
The watchdog found ex-departmental general manager of business integrity Mark Withnell carried out corrupt conduct by intentionally misleading the Department of Social Services during the preparation of a cabinet submission in 2015.
It also found department deputy secretary Serena Wilson carried out corrupt conduct by misleading the Commonwealth Ombudsman during an investigation in 2017.
But the watchdog said the findings won't be referred to the Commonwealth Department of Public Prosecutions to consider criminal charges.
"There was insufficient admissible evidence to establish the alleged offences against either Mr Withnell or Ms Wilson beyond reasonable doubt," the report said.
"Key admissions and statements made during this investigation are not admissible in criminal proceedings."
Mr Morrison was not found to be corrupt.
His failure to realise bureaucratic advice was misleading was put down to shortcomings by federal departments.
The corruption watchdog did not make recommendations in its final report, which followed referrals from the royal commission into the robodebt scheme.
The watchdog initially chose not to investigate the referrals before the controversial decision was overturned.
The over-ruling came after National Anti-Corruption Commission Inspector Gail Furness found commission head Paul Brereton engaged in misconduct because he had ties with one of the six officials but did not adequately recuse himself from decisions.
Between 2016 and 2019, the former coalition government's robodebt scheme recovered more than $750 million from almost 400,000 people.
Many welfare recipients were falsely accused of owing the government money and the program was linked to several suicides.
The Albanese government has promised it will release a sealed section of the robodebt royal commission's final report when the investigation ends.
The robodebt scheme was a betrayal of everyday Australians and resulted in human tragedy and untold misery, Attorney-General Michelle Rowland said.Â
"The royal commission was clear in its findings and we must work to ensure this can never occur again," she said.
Greens senator Penny Allman-Payne said the findings of the corruption watchdog would be cold comfort to robodebt victims.
"There may be some small satisfaction found in the fact that two staff were found to have acted corruptly, but the architects of robodebt are still sitting pretty," she said.
"No government minister has been held accountable, which means no government has been held accountable."
Independent MP Helen Haines, who was one of the key advocates for the establishment of a federal corruption body, said the findings were welcome, but the investigation should not have taken so long.
"The fact a second investigation was required highlights the importance of scrutiny and transparency in the work of the NACC," she said.
"Without the sustained public pressure that led to a review of the earlier decision, those impacted by robodebt may never have received the validation that this finding now provides."
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