Lawyers for the construction union have raised concerns about changes to the formal police account of a raid on its Canberra headquarters, in attempt to have the evidence seized struck out.

The CFMEU has launched action in the ACT Supreme Court over the legality of the raids on its Dickson offices in August, following evidence of alleged blackmail heard during the royal commission into trade union corruption.

Its lawyers argued police went beyond the bounds of a search warrant and did not allow union staff to properly observe the raids.

The CFMEU's lawyer, Peter Morrissey, said police evidence changed after the release of surveillance footage of the raids.

"It was only once the CCTV footage was revealed that there was any acknowledgement that any sort of impediment [to union staff] was imposed," he said.

"It was somewhat troubling that the safety and procedure excuse emerged later and in the terms that it did."

He said the alleged problems with the search meant the material seized should be inadmissible.

"We'd say that what follows from there is the search is invalid and the seizures made there under [it] are invalid," Mr Morrissey said.

Role of the bomb squad questioned

Mr Morrissey also questioned what the AFP bomb squad was doing at the raids.

The AFP's lawyers said on Monday the bomb squad was present during the search with equipment that could have posed a threat to the safety of bystanders, which was why union officials had their movements restricted.

But Mr Morrissey showed surveillance footage today that he said showed the only items the bomb squad brought into the building were a ladder, goggles, coffee and takeaway food.

One of the police officers involved in the search, Detective Senior Constable Gregory Adams, suggested one member of the bomb squad was also carrying an unknown device with a green case.

But acting Chief Justice Richard Refshauge was sceptical of that claim.

"It looks to me like a mobile phone," he told Detective Senior Constable Adams.

"It may not be. It may be a magic bomb squad device."

The AFP has maintained that police followed standard procedure during the raid.

Police defend CFMEU raids

Several police officers, including Operational Commander Sergeant Scott Utteridge, were questioned today.

Sergeant Utteridge defended the number of police he allocated for the job and said he had initially thought they would get through the task by 5:00pm.

But the court heard the raids stretched on into the night and Sergeant Utteridge decided there was not enough time to make immediate copies of the documents seized.

"I made a decision based on information available to me at the time," he said.

"I'd never been to the address of interest so I wasn't really sure what the scope of the requirements would be."

He also responded to questions over a police failure to search several CFMEU officials and said he did not ask his officers whether it had been done.

"We're talking about experienced members here," he said.

"I don't micromanage these guys."