A man has been found guilty of murdering an 11-month-old boy at Paynesville, with the court being told the child's injuries were so significant he would have bled out in tens of seconds.

A jury took about 24 hours to find Jason Noy, 28, guilty of the murder of Harro Dean at their Paynesville home, in Victoria's east, in July 2016.

The Supreme Court sitting in Morwell heard the infant died from massive internal bleeding.

Prosecutor Andrew Grant told the court that Harro suffered "a constellation of injuries" and Noy was the only person there with the opportunity and ability to inflict those injuries.

Noy will be sentenced on June 20.

'We never see this', forensic pathologist says

Paramedics were called to the home shared by Noy and Harro's mother Jamee Malcolm about 7.30pm on the night of July 5, 2016.

Harro was pale and non-responsive. He was pronounced dead at the Bairnsdale Hospital at 9.09pm.

Harro Dean (R) was 11 months old at the time of his death in 2016. ( Supplied: Facebook )

The forensic pathologist who examined Harro's body, Heinrich Bower, said the child's injuries were so significant he would have bled out within "tens of seconds, minutes at most".

Dr Bower told the court it was almost unheard of to see that type of injury in that setting.

"It's very rare, we never see this," he said.

He told the court Harro would have been "in excruciating pain" and it was impossible for someone to inflict the injuries by accident.

Dr Bower said the force required to inflict Harro's injuries was "at the farthest scale of severe, even past severe", and would have involved the hyper-extension of his back.

The jury was told Noy's version of events was "impossible" given Dr Bower's evidence, and Mr Grant described his account as "an elaborate lie".

Noy denies hurting baby

Noy has consistently and repeatedly denied that he did anything to hurt Harro.

Noy said Harro "was sort of cracking it" while he changed his nappy, so he gave him his blanket and laid him in his cot before leaving him alone to warm up a bottle of milk.

He said when he returned, Harro was "laying weird … like he was being strangled, but he wasn't".

In his interviews with police in the days after Harro's death, Noy repeated what he had told paramedics who attended, telling them he did not know what had happened to Harro, only that he "didn't do it".

However, he told Detective Senior Constable Mark Berens that he "knew [he] would get the blame for it".

Jason Noy arrives at the Bairnsdale Court in June 2017. ( ABC Gippsland: Melinda Ogden )

"I mean look at me," Noy said. "I get judged on my appearance all the time."

His defence lawyer, David Gibson, told the jury that Noy was "unwavering" in his explanation, and there was "no direct evidence about that implicates Jason Noy in the murder of Harro Dean".

The jury heard Noy was alone with Harro while Ms Malcolm was at the opposite end of the house, helping her daughter get ready for bed.

"If anyone could point the finger at Jason Noy for the murder of her son, it would be Jamee Malcolm," Mr Gibson told the jury.

"If something catastrophic had happened in the house, Jamee must have heard something.

"But she saw and heard nothing."

Mr Gibson did not offer an explanation as to how Harro had suffered his injuries, but said it was "like a tragedy that came out of nowhere".

'Clearly an unusual relationship'

The court heard Noy had been involved in a relationship with Ms Malcolm, but the relationship was over before the boy's death.

Despite this, they continued to share a bed and caring duties for Harro and his older sister.

Mr Gibson acknowledged that it was "clearly an unusual relationship", but Noy continued to help raise Harro and treat him as his own son.

But Mr Grant said Noy "knew Harro, he knew how fragile he was".