A former senior staffer in Federal Minister Michaelia Cash's office has told a court he knew a media tip-off about police raids on union offices would be politically damaging for Opposition Leader Bill Shorten.

Key points: The AWU is seeking to shut down the ROC's investigation into donations the union made to GetUp! in 2006

The AWU is seeking to shut down the ROC's investigation into donations the union made to GetUp! in 2006 Senator Cash referred the donations to the ROC in two letters in August 2017

Senator Cash referred the donations to the ROC in two letters in August 2017 Her then-media advisor alerted media outlets to the raids before they started

Australian Federal Police raided the Sydney and Melbourne offices of the Australian Workers' Union (AWU) on October 24, 2017, as part of an investigation by the Registered Organisations Commission (ROC) into $100,000 in donations made by the union in 2006, when Mr Shorten was its national secretary.

Ben Davies, who was Senator Cash's chief of staff at the time of the raids, is giving evidence in a civil trial brought by the union against the ROC, which has been investigating the union's donations to the activist group GetUp!.

The court has previously heard that on the day of the raids, Senator Cash's then-media advisor, David De Garis, contacted media outlets to give them advance warning of the raids.

Federal police officers raided the Sydney and Melbourne offices of the AWU as part of the ROC investigation. ( AAP: Julian Smith )

Mr Davies agreed with the AWU's lawyer Herman Borenstein QC that the presence of TV crews at the union's offices as the AFP seized documents relating to the donations was "to the political detriment of Mr Shorten".

"The political implication was that the investigation related to donations made during the period Mr Shorten was responsible for the AWU … and questions about whether they had been authorised," Mr Davies told the court.

Who's who in the witness box: Senator Michaelia Cash: WA Senator who was the Federal Minister for Jobs at the time. She has repeatedly and vehemently denied knowledge of the media tip-off, which came from her office.

WA Senator who was the Federal Minister for Jobs at the time. She has repeatedly and vehemently denied knowledge of the media tip-off, which came from her office. David De Garis: Senator Cash's media advisor at the time who admitted to tipping off the media, and resigned. He now works for the Australian Hotels Association based in Perth.

Senator Cash's media advisor at the time who admitted to tipping off the media, and resigned. He now works for the Australian Hotels Association based in Perth. Mark Lee: Media advisor at the time at the Fair Work Ombudsman which also assists the Registered Organisations Commissioner. He was formerly a media advisor to the former Victorian premier Denis Napthine. At the time of the raids he was expecting to join Senator Cash's office as a media advisor, but after the raids that did not happen.

Media advisor at the time at the Fair Work Ombudsman which also assists the Registered Organisations Commissioner. He was formerly a media advisor to the former Victorian premier Denis Napthine. At the time of the raids he was expecting to join Senator Cash's office as a media advisor, but after the raids that did not happen. Ben Davies: Chief of staff for Senator Cash at the time. He left the office a few months later. In 2011, he worked in the office of Victoria's then attorney-general, Robert Clarke.

Chief of staff for Senator Cash at the time. He left the office a few months later. In 2011, he worked in the office of Victoria's then attorney-general, Robert Clarke. Chris Enright: Executive director of the Registered Organisations Commission who wrote to the AWU two months before the raids advising of the ROC investigation

The court has previously heard Mr Davies passed on information about the raids to Mr De Garis after being alerted to them by Mark Lee, who was on secondment to the newly established ROC at the time and had been offered a job in Senator Cash's office.

Mr Davies said he received a call from Mr Lee on the day of the raids.

"He volunteered information to the effect that the ROC was conducting an investigation into the AWU … [and] that the ROC had heard from a whistleblower that the AWU was seeking to destroy documents," Mr Davies said.

"The information supplied was unsolicited, unprompted and unexpected."

Mr Davies said he was concerned the AWU may have been engaged in the destruction of evidence in order to benefit Mr Shorten.

When asked whether he had considered whether the media tip-off could compromise the police operations, Mr Davies said: "During that discussion I did not turn my mind to the broader implications."

Last week, Senator Cash rejected assertions that Mr Shorten was personally targeted and that she was politically motivated in referring concerns about the donations to the ROC via two letters in August 2017.

She told the court she was carrying out her ministerial responsibilities after concerns were raised in a newspaper article about the use of members' funds.

Senator Cash told the court on Friday she was not politically motivated in referring the donations to the ROC. ( AAP: David Crosling )

Mr Davies said he did not advise Senator Cash of the tip-off to the media on the day of the raids.

Mr Lee is also expected to give evidence in the trial later this month.

The court heard Monday Mr Lee had been offered a job in Senator Cash's office in the week before the raids.

Labor seizes on court evidence

Labor senators seized upon the evidence from the Federal Court, grilling senior Australian Federal Police officers appearing before a Senate committee in Canberra.

Queensland senator Murray Watt questioned Deputy Commissioner Leanne Close about the Commonwealth Director of Public Prosecutions' decision not to press charges against anyone involved in the incident.

"We also work with the Commonwealth DPP, and they are the authority to determine whether a prosecution should proceed or not. So we accept their advice," Deputy Commissioner Close said.

Senator Watt asked whether the AFP still believed a prosecution could be successful, if pursued.

"If we had all of the information available to the Commonwealth DPP, yes," Deputy Commissioner Close responded.

The AFP also confirmed it believed some evidence relating to the case had been destroyed.

Last week, Senator Cash's former media adviser confirmed he had deleted text messages relating to the leaks.

"We did find some of that material may have been destroyed," Deputy Commissioner Leanne Close told Senate estimates.

AFP not ruling out reopening leaks investigation

AFP Commissioner Andrew Colvin would not rule out reopening the police investigation into the leaks, given the evidence in the Federal Court.

"It always remains a possibility at any point to reopen an investigation, I'm not going to say if we do or do not intend to re-open," he said.

Mr Shorten said the evidence was clear.

"The court case has managed to find out information that the AFP couldn't find out," he said.

"So I'd be interested to know the answer of the AFP.

"How is it that the union, through a court proceeding, could find out who did these things and the AFP couldn't?"