Malcolm Turnbull wants heads to roll over the leak of thousands of cabinet documents accidentally sold in a locked second-hand filing cabinet.
"This is a disgraceful, almost unbelievable act of negligence," he told ABC TV on Sunday.
"The idea that public servants, entrusted with highly confidential documents, would put them in a safe, lock the safe, lose the keys, and then sell the safe without checking what was in it - it beggars belief.
"Seriously, if you put it in an episode of Utopia or something like that, I imagine an editor or producer would have said, 'No, that stretches credulity. Take it out.'," he said.
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The prime minister's own department struck a deal with the ABC for the secure return of the documents and was investigating, along with the federal police, how they came to be in the hands of a member of the public in the first place.
The ABC had on Wednesday revealed papers covering details of five federal government cabinet meetings over a decade had been unsuspectingly sold off in a pair of locked filing cabinets at a second-hand shop in Canberra, which stocked ex-government furniture.
The filing cabinets were unlocked with a drill months later.
Cabinet papers usually remain secret for 20 years.
Mr Turnbull said the timeline of the events hadn't yet been established and he understood the most recent documents in the stash dated from early 2014 - before he took over as prime minister.
Nevertheless, he said he wanted to see heads roll over the "shocking failure".
