Three people who went missing during the deadly 2011 Grantham flood have never been found, an inquiry in Queensland has heard.

Detective Inspector Dave Isherwood was involved in Taskforce Galaxy, set up to search for the 572 people reported missing after the January flood west of Brisbane, which officially claimed 12 lives.

He told the Grantham Floods Commission of Inquiry that police and other government agencies crossed people off that list after seeing them or speaking with them by phone.

"The enormity of actually trying to physically sight everyone at that stage would've been time consuming," he said.

The inquiry heard police also searched 767 flood-affected vehicles in Toowoomba and the Lockyer Valley.

"The reason we looked at those vehicles is ... because people were seen in vehicles being washed away," Detective Inspector Isherwood said.

"We were concerned that perhaps there may have been deceased people in vehicles."

Detective Inspector Isherwood's statement to the inquiry detailed where the bodies of 12 people were found.

"Three people [are] still missing as a result of the disaster," he said.

"Two of those people are from Grantham, and one person was washed away on the Warrego Highway."

Flood-affected people do not hold blame for police

A lawyer representing 17 people affected by the floods told the inquiry his clients did not blame police for their limited investigation into flood fatalities.

Nathan Turner said his clients understood police had a difficult role in the days following the tragedy.

"This was a massive natural disaster," he said.

"You can understand why police's main focus was trying to save people, then find bodies."

He said police were hampered because the state government announced the 2011 Queensland Floods Commission of Inquiry just seven days after the Grantham disaster.

"So from that point on you can understand why the police would've felt like they were under the direction of others," Mr Turner said.

He said the surviving residents of Grantham believed it was more than just the rain event and the natural landscape that caused the flood.

The inquiry heard police took 854 witness statements in the days following the flood but only one mentioned embankment walls surrounding the Grantham quarry.

"But you have to remember that when a statement is taken, particularly by police officers in this environment, and certainly no criticism of them, they are wanting to capture certain information and their mind may not have been focused on other information," Mr Turner said.

"[My clients] weren't to know at that stage that potentially there was something else that caused this flood, it wasn't just a natural feature of the landscape."

Detective Inspector Isherwood told the inquiry the terms of reference of the 2011 inquiry limited the police investigation to the basic facts about each fatality.

"Police investigated as they normally would," he said.

"But where questions may have been asked about certain things, we may not have asked questions."

Video evidence cannot be found: inquiry

Detective Inspector Isherwood told the hearing he was also part of Operation Juliet Drew, which helped establish exclusion zones around Grantham, coordinated the recovery of lost property and took witness statements.

"If people supplied photos or digital imagery, usually a statement was taken from the person," he said.

He said most of the images and vision were stored in the Queensland Police Service's IMAC system, and more than 100 items were received on CD, DVD or printed images.

Counsel assisting the inquiry Michael Hodge quizzed Detective Inspector Isherwood about one piece of evidence that went missing.

"It was video showing people crossing the railway bridge to escape the flood," Detective Inspector Isherwood said.

"The video was taken by a resident who was being harassed by media.

"She gave it to a Queensland Health counsellor who gave it to a police officer, who then passed it onto another junior police officer, who didn't lodge it as evidence.

"Instead, it was lodged as lost property and it can't be found."

The inquiry is examining whether natural or manmade landmarks contributed to the deadly flood.

It has previously heard evidence from local residents, who claim embankment walls at the Grantham Quarry worsened the disaster.

Former quarry owner Denis Wagner has denied the allegations.

The inquiry continues.