It was standing room only as the verdict was delivered to a packed Supreme Court in Brisbane, with members of the gallery breaking down as the four were found guilty.

Stou Daniels, Davy Malu Junior Taiao, Trent Michael Thrupp and Waylon Ngaketo Cowan Walker had denied murdering Cory Breton and Iuliana Triscaru south of Brisbane on January 24, 2016.

Daniels, Taiao and Thrupp were found guilty of two counts of murder.

However, Walker was cleared of the murder charges, but convicted on the lesser charge of manslaughter.

During the trial, crown prosecutor David Meredith said all of the people involved were dealers and users of drugs.

The court was told the motive stemmed from a photograph of a smiling Daniels captured on CCTV on January 22 - two days before the murders.

The owner of a convenience store owner who sold burner phones and purchased drugs from Mr Breton asked him where he sourced his drugs and was told "Islanders".

The owner then sent Daniels' CCTV image to Mr Breton, asking if "that was him".

Mr Breton replied: "Yes, that's him".

Daniels became wary when told about the photo and was convinced he was being set up, the court was told.

"The prosecution says that the motive for all of this was Daniels being suspicious of Cory Breton," Mr Meredith said.

The victims were lured to a Kingston unit, tortured, assaulted and bound with tape and zip ties before being put in the toolbox, Mr Meredith told the jury in his opening.

The box was put onto the back of a ute and dumped in the Scrubby Creek Lagoon, south of Brisbane.

More than two weeks later, on February 11, police divers found the bodies in the box - weighed down by concrete blocks and tyres.

The bodies were so badly decomposed doctors could not determine a cause of death, only that the pair could have died from asphyxiation or drowning.

"The evidence seems to be that they were still alive when they were put into Scrubby Creek," said Mr Meredith.

"According to witnesses, they were still yelling and kicking at the toolbox when they left the apartment complex."

Toll cameras captured images of the utility with the toolbox strapped to the tray on the Logan Motorway about 8.50pm before the toolbox was dumped in the lagoon.

"If these things are true this killing is extraordinarily barbaric," Mr Meredith said.

"These people were put into a toolbox and kept there for several hours - obviously fearing what might happen to them.

"They were taken to a creek and drowned ... it's breathtakingly evil."

Lawyers for the accused had urged the jury to keep an open mind, saying key witnesses in the Crown case had mental health issues with a history of drug and alcohol abuse.

However, after the jury retired at 11.45am on Thursday, it reached its verdict within hours.

The four will be sentenced on March 15.

Australian Associated Press