Dr Naren Gunja gave evidence on Tuesday during the trial of Benjamin Batterham, who has pleaded not guilty to murder over the death of Richard Slater, who was found breaking into Mr Batterham's Cleary Street home in March, 2016.

Mr Slater had 0.71mg/L of methylamphetamine and 0.05mg/L of amphetamine in his system, a pre-existing heart condition, obesity and was chased 330 metres from the home to where he was allegedly tackled, pinned down and repeatedly punched by Mr Batterham.

The central issue in the trial is Mr Slater's cause of death, with Dr Gunja disagreeing with all the other medical experts about the extent that the level of methylamphetamine contributed to Mr Slater's death.

The jury has, so far, heard from one other medical expert, forensic pathologist Dr Jane Vuletic, who opined that Mr Slater's pre-existing heart condition combined with a "potentially lethal" level of ice in his system was more likely to have caused his death than being placed in a "choke-hold".

And, according to excerpts from other expert medical reports referred to already in evidence, the trial is expected to hear from a number of other doctors who disagree with Dr Gunja and say methylamphetamine either contributed significantly or was the primary cause of Mr Slater's death.

When asked his opinion as to Mr Slater's cause of death, Dr Gunja said a hypoxic brain injury - a restriction of the flow of oxygen to Mr Slater's brain - caused his death.

"The brain didn't receive enough oxygen," Dr Gunja said. "While there may have been contributory factors, such as the effects of running and the methylamphetamine. "There was a clear precipitant... he had a constrictive force around his neck, he had been placed in a prone position with his arm pinned down. He would not have been able to take deep breaths and would have had asphyxiation from that."

Dr Gunja said due to Mr Slater's "normal" body temperature that methylamphetamine toxicity was "unlikely". The trial continues.