The federal infrastructure department hired an independent auditor to do further checks on a controversial Western Sydney Airport land deal after the auditor-general found problems with it.
The department in 2018 paid $30 million for land worth $3 million near the airport development.
The Australian Federal Police is investigating potential fraud involved in the deal after Auditor-General Grant Hehir referred it to them in July.
A Senate estimates committee heard on Tuesday the department felt the initial audit left some "outstanding questions" to be resolved.
Department secretary Simon Atkinson said the auditor-general probe was focused on "documentation", but he was keen to find out "what happened beyond the documents".
"There were so many direct allegations around what people knew," he said.
"We wanted a full perspective on what happened to support future management decisions and improvements."
He said there were also questions around the "culture" of the organisation that needed to be examined.
"Any organisation that has something like this happen should look if there is a cultural element to it."
Labor's Penny Wong asked whether one of the officials stood aside from Western Sydney Airport had gone on to work with the multi-billion-dollar Inland Rail project.
Mr Atkinson declined to publicly comment, but offered to give evidence in private.
"We are trying to protect the privacy of the individual under investigation."
The committee heard AFP officers had been provided with a large amount of material from the auditor-general and given three names of people to interview - one currently serving official, one former official and the independent auditor.