The Wodonga company has been accused of failing to ensure people were not exposed to health and safety risks, in the way it serviced a truck and trailer.

The trailer carrying a BP fuel tanker detached from a truck at Staghorn Flat on August 7, 2014, causing the deaths of three other people on the road.

The jury in a trial held in November was discharged before a verdict was reached.

Prosecutor Andrew Palmer, QC, told the County Court on Thursday that expert witness William Kennedy conducted further tests since November and would expand his evidence for the retrial.

He also wanted to use a new witness to rebut the defence, which had questioned the character of the mechanic during the first trial.

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Barrister representing Heavy Mechanics Daniel Gurvich, QC, said it was "unacceptable" for changes to be made so late.

"It's unfair, it's oppressive to our defence and undermines the course of justice in a serious way," he said.

"The Crown should not be permitted to rely on the second Kennedy statement."

He wanted only the video evidence from the first trial played for the new jury.

Mr Palmer said it was not unusual for changes to happen in retrials. "The prosecution does not accept at all that there was an abuse of process here," he said.

Judge Gerard Mullaly said he needed time to consider the arguments before making a decision and adjourned the case.

The retrial is due to begin on April 20.