The land purchase, which the ACT Auditor-General Maxine Cooper is now investigating as part of a wider audit into LDA rural land purchases, began in early March 2016.

But over a year later, after an earlier damning audit into controversial LDA land deals highlighting the agency's "loose governance" arrangements, Mr Barr on May 1 last year approved the purchase under those same rules.

Answers to questions on notice posted during annual report hearings of the Assembly's planning committee have shed further light on the deal sealed on the final day of the LDA's operations, June 30 last year.

Those answers, to questions from Canberra Liberals MLA Elizabeth Lee, show the then-landowner of the Mount Stromlo property, Winslade, first approached the LDA with the offer to sell on 11 March 2016.

In June 2016, the LDA's board considered the acquisition, directing the former agency's staff to complete a more detailed assessment of the proposed purchase.

The answers also show the purchase was consistent with the old LDA's land acquisition policy, including a due diligence assessment and a business case that was prepared for Mr Barr as Treasurer.

But the old land acquisition policy demanded only one valuation of the purchase, compared to the two valuations and greater transparency and integrity measures that are now in place for the CRA and Suburban Land Agency.

That valuation, by Knight Frank, put the package of Stromlo rural blocks 435, 439, 440, 441, 456 and 476 at a total of $7.5 million in May 2016, with $368,250 of stamp duty and various smaller associated regulatory fees.

It remains unclear why Mr Barr approved the purchase based on a year-old valuation and within two months of the former LDA being abolished; instead of waiting to ensure the purchase would be consistent with the more stringent requirements.

While planning officials told an Assembly committee hearing last year they did not know what purpose the land would be used for, the answers also show that "the LDA considered the potential use of land for future urban growth".

The answers to the Questions on Notice showed that LDA's assessments of the massive rural land package also 'has potential to yield a positive financial outcome for the territory".

"Winslade is strategically located between properties previously acquired by the LDA," the document reads.

"Acquiring this property would provide opportunity for infrastructure connections between these two areas".

Mr Barr did not directly answer questions including why the land was purchased only weeks before more stringent arrangements began, whether the purchase was in ACT taxpayers' best interests.

Instead, his spokesman said the purchase was "unrelated to organisational changes" at the LDA and that the purchase was assessed, including a due diligence process, under the former land acquisition policy.

"The government considered all of this information, and the advice of the Treasury, in deciding to progress with the purchase," he said in a statement.