Canberra: A 1,000-page manual containing confidential security measures for Australian parliament house’s multi-million security dollar upgrade has been lost by a contractor and not reported missing for three months.

Officials from the department of parliamentary services have defended the document’s loss under sustained questioning from Labor senator Kimberly Kitching during Senate estimates hearings on Monday. They revealed a private investigator was hired to find it but did not succeed.

The document contains information about parliament house’s $126m security upgrade that is not available to the public, and DPS officials confirmed it had been lost by a contractor in November 2016, but not reported as being “misplaced” until February 2017.

Senate president Stephen Parry, has faced questions from Kitching and Labor senator Penny Wong about the missing manual, claimed parliament house’s security “has not been compromised”, though he admitted he had no idea of the manual’s whereabouts.

To allay the public’s fears, he said it wasn’t completely clear if the manual was not in the DPS’s possession.

“You’ve indicated a manual is lost,” Parry said. “There is no indication or confirmation that the manual has gone anywhere ... as in, there’s no indication it’s gone into [public] hands.”

In a tense to-and-fro with committee members, Parry and DPS officials were adamant that the contents of the document should not be discussed on the record.

Wong pressed DPS officials about the curious case of who may have the document.

“As I understand the president’s evidence, he is saying we can’t find any evidence that it has got into the hands of someone untoward, but we don’t know where it is, so we don’t know who’s got it. Is that right?” she said.

A departmental official said the manual was “definitely lost”. That led Wong to conclude that “by definition, that means we don’t know where it is.”

Parry came to the defence of the department, downplaying the importance of the information in the document, saying the security measures related to “matters that would have taken place in the future”, not current arrangements for parliament house.

He said after the private investigator — who had been contracted to look for the document from February 27 to March 23 — failed to find anything, it had been determined that the document was not that important.

“It was an early draft ... some of the portions in that early draft are now redundant ... a number of aspects have been modified, and about 50% of the materials are commercially available products,” Parry said.

“Once the investigation was completed, our fears were allayed considerably.

“However, we still don’t want to identify aspects of this so people don’t go looking in areas that we don’t want people to go looking in ... just in case some matters are discovered.”

Wong replied: “You’re comfortable there’s no compromise despite the document being lost and you not being able to tell who has access to it?”

Parry: “Correct. But also I’ve just outlined our concerns have been allayed somewhat because of what is actually in that draft.”