Officials at Parliament House concede they have no idea who has possession of a 1000-page security manual lost in November last year, despite calling in private investigators.
Labor senator Kimberley Kitching used Senate estimates hearings on Monday to reveal the sensitive security manual had been lost by a "private entity", and ask officials from the Department of Parliamentary Services why an investigation was not launched until February.
Senate President Stephen Parry said there was no indication security had been compromised but the investigation had failed to find the sensitive material.
The Australian Federal Police were informed the contractor had lost the manual, but senior political figures including Prime Minister Malcolm Turnbull, Attorney-General George Brandis and Justice Minister Michael Keenan were not immediately informed.
The manual was lost by a company involved in security upgrades at Parliament House.
"There has been no compromise to the Parliament House security," Senator Parry said.
"There is no indication or confirmation that that manual has gone anywhere... I don't want to leave it out there that this manual is somewhere out there in the public domain."
He said the manual dealt with security matters in the future.
"Not matters that had actually taken place, which gives the department the opportunity to modify and change," he said.
"It was an early draft, a lot of the matters are now redundant, a lot of the matters have been modified and over 50 per cent of the materials which were going to be sourced were commercially available.
"It is not a breach of security and security at Parliament House has not been compromised."
Officials told the hearing an investigation was completed between late February and March 23, with the AFP providing advice on the private investigator chosen for task.
Department of Parliamentary Services first assistant secretary Paul Cooper, who oversees security, said the investigation had been conducted as if a "worst case scenario" had taken place.
He said it found there had been "no substantial breach of security".
"Often is the case with these things that the conclusion turns out to be far less concerning than it may have looked, but we are obliged to take the worst case scenario with these matters and have them investigated in the way we did," he said.
Asked if the manual had been found, Senator Parry said he didn't know where it was.
"It is definitely lost," he said.
A $126 million security upgrade is under way Parliament House, including a 2.6 metre-high steel fence across the sloping front lawns.