The Public Accounts Committee (PAC) said it is done with questioning former Treasury secretary-general Mohd Irwan Serigar Abdullah over the allegedly missing GST refunds.

Next up to be questioned by the PAC will be former prime minister and former finance minister Najib Abdul Razak.

“I think we have called Irwan twice so we have got whatever information or testimony needed from him.

"This afternoon we will be calling Customs director-general Subromaniam Tholasy, and tomorrow, it will be former finance minister Najib," PAC deputy chairperson Wong Kah Woh said in the Parliament lobby today.

He was speaking to reporters after the PAC concluded its meeting with Irwan at the PAC committee meeting room in Parliament.

PAC chairperson Ronald Kiandee said today's proceeding was a short one as they were only asking follow-up questions based on Irwan's first testimony.

"On GST refunds, we hope we will conclude and wrap-up this case before the end of this parliamentary sitting.

"After the last witness, who is the present finance minister, we will wrap up the case and present the findings to Parliament," Kiandee said.

This PAC probe is in relation to Finance Minister Lim Guan Eng (photo) telling the Dewan Rakyat in August that a Customs Department audit had revealed that the total GST refunds amounted to a mere RM148.6 million, from the date of its implementation, until May 31, 2018.

Lim had initially stated the bulk of the RM18 billion sum was unaccounted for and had been "misused" by the previous administration.

He later amended the shortfall to RM19.248 billion, attributing the mistake to a decimal error made by an official of his ministry.

The PAC investigation has also received testimonies from former second finance minister Johari Abdul Ghani and former second finance minister Ahmad Husni Hanadzlah.

Wong also told reporters today that PAC is working towards opening up its proceedings to the public, as long as security issues are not touched on.

However, he said, there were legal obstacles in the way, such as Order 85 of the Standing Order and Section 9 of the Parliament Rights and Privileges Act, which prevent the opening up of the PAC proceedings to the public.

"We are still working towards that (opening up PAC meetings) and we all feel that things should be open towards a First World Parliament," he said.

Subromaniam gave his testimony to the PAC this afternoon beginning at 2.30pm and ending at around 3.15pm.

As with Irwan, Wong said this was Subromaniam's second testimony to the PAC as they wanted some clarifications.

They will not be calling him for another testimony after this, he said.