Australian Federal Police investigators found there was no criminal or malicious intent involved as the department lost the files, obtained by the ABC and leading to an inquiry into the cause of the high-level bungle.

Department of Prime Minister and Cabinet secretary Martin Parkinson reported the results of the AFP probe on Friday and released in full a review urging reforms to its security measures to prevent a repeat of the episode, which saw ASIO raid the national broadcaster's offices to secure the top secret and classified files.

Dr Parkinson said he had "personally dealt with" and sanctioned officials for their roles in the breach.

The AFP finished its investigation in March, finding the massive leak resulted from "a culmination of human errors" in PM&C;'s record-keeping and in its movement, clearance and disposal of storage containers in February 2016.

Federal police decided to lay no charges but the nature of their findings have remained unknown since they were handed to Dr Parkinson, Australia's most senior public servant.

He has been under pressure to explain how the documents disappeared from within his department inside a locked cabinet sold at a second-hand furniture sale in Canberra, ultimately winding up in the hands of ABC journalists.

The furniture was bought on the cheap by a "bushie", who discovered the documents inside and gave them to the ABC, which in January published stories covering the lost documents.

Described as one of the biggest national security breaches in Australian history, the Cabinet Files revealed secret cabinet discussions during the Howard, Rudd, Gillard and Abbott governments.

Dr Parkinson said the AFP's report would not be made public but that he had accepted the findings of a review by former Defence Department secretary Ric Smith, handed over in March, urging change to PM&C;'s handling of documents.

"I am deeply concerned that such an extraordinary lapse of security could occur," Dr Parkinson said.

"I am committed to ensuring that such an unauthorised disclosure does not happen again and that the lessons from this are disseminated and absorbed across the entire Australian Public Service."

PM&C; is digitally tracking its secure cabinets, has revised rules about handling them, and will audit their security.

Staff will also undertake training and have been told to check their filing cabinets, secure containers and desks to see if classified information was stored or disposed of correctly.

The Smith review urged the department to bolster and modernise its security following the leak, saying staff responsible for breaches should be counselled and recommending those guilty of three incidents in a year face potentially job-ending reviews of their security clearance.

Federal police confirmed after their inquiry the 300 documents, collated between 2013 and 2014, came from the section responsible for Freedom of Information requests within the cabinet division at PM&C;, in its offices at One National Circuit in Canberra. Some of the documents were classified for national security reasons.

The AFP found the documents left the Prime Minister's department in early 2016 after its cabinet division moved and eight secure containers were identified as surplus and returned to another division.

"PM&C; has concluded that the secure containers were not checked to ensure they no longer held any documents," the Smith review said.

"Email records indicate that two secure containers in cabinet division – formerly used by the officer, or officers, who collated the documents – were missing keys at the time they were being prepared for disposal. There is no record that the containers were opened and checked prior to disposal."

Mr Smith recommended a second review in a year's time and Dr Parkinson has asked other government agency bosses to audit their own departments' disposals of secure containers.