The 34-year-old Wangaratta man died on or about July 26 last year and the two men charged over his alleged murder - Phillip Dunn, 59, and Darcy McNamara, 43 - faced the first day of a two-week committal hearing on Monday.

Neither have entered any pleas.

Forensic pathologist Paul Bedford told Wangaratta Magistrates Court that Mr Day died from a wound to the neck, nine centimetres wide and two centimetres deep.

He said "it was caused by a sharp implement", which could have been a knife.

The wound was to the right side of the neck, cut horizontally and slightly upwards.

Dr Bedford said it would have been second to minutes before blood was lost to the brain.

"The bleeding would be rapid," he said.

He said a bone was also broken on the same side of the neck, which could have been caused by the force of a knife.

Asked by McNamara's defence barrister Jarrod Williams if the wound was stabbing or cutting, Dr Bedford said "either is possible, but there is a degree of stabbing".

It was six weeks after Mr Day was last seen that his body was found buried in the backyard of McNamara's Ryan Avenue home on September 5.

His mother teared up in the courtroom as she heard the details of what allegedly happened to her son.

It was revealed investigators tested for Mr Day's DNA inside Dunn's home, also on Ryan Avenue, but could not find anything conclusive.

There was however strong evidence that Mr Day's DNA was in the home of McNamara at some point.

MORE NEWS FROM COURT:

The autopsy revealed Mr Day had an alcohol level of 0.29 in his blood, and 0.25 in his urine, when he died.

Dr Bedford said even though the body had started decomposing over the previous six weeks, the figure was "in the ballpark".

But toxicologist Kerryn Crump said alcohol levels can rise in body after a person has died, so she could not say if the number was the same at the time of death or how many drinks Mr Day would have consumed.

"It does cause difficulty in analysing the results," she said.

"We know there was a presence of alcohol in the urine so we know that at some stage, alcohol was taken ... but the level I cannot comment on."

Dunn's barrister Diana Price said witnesses in the trial would give evidence that "Mr Day drank alcohol frequently, to excess".

Ms Crump said cannabis and opioids - possibly morphine, codeine or heroin - were also detected in Mr Day's urine.

Forensic expert Jeanette Psaroudis also said semen was detected in Mr Day's body, but there was not enough evidence to identify the DNA.

It was during an "overly flirtatious" conversation with a female police office that Phillip Dunn decided to tell police that Darcy McNamara killed Nathan Day.

First Constable Lisa Thompson gave evidence on Monday that Dunn stumbled into the path of the police divisional van she was driving in a Benalla car park.

She said he smelled heavily of alcohol when she started talking to him and he asked her out on a date.

But it was when she asked how he got a cut on his cheek that he decided to talk. "I like you, I know about a murder I want to tell you about," Dunn told Constable Thompson.

He said "I saw it, he was still kicking" when describing Mr Day's alleged murder and was immediately taken back to Benalla police station to be interviewed by detectives.

Constable Thompson stayed in the room during the interview because Dunn was comfortable around her.

"He was cagey, but still forthcoming," she said.

Both Dunn and McNamara were charged with murder on September 6.

Dunn kept his head down in the dock during the officer's evidence, while McNamara - sitting in the body of the court flanked by police custody officers - kept his head up but did not show any emotion.

The pair lived in the same street in Wangaratta and, according to Leading Senior Constable Marielle Porter, had a "not very amicable" relationship.

The court heard that around the time of Mr Day's death, both men had accused the other of breaking windows at the their homes.

Leading Senior Constable Porter said at one stage the men were screaming at each other from across the road while police were there to respond to the complaint.

"(Dunn) just came across as an agitated, angry person," she said.

The committal hearing has been set down for 10 days and continues on Tuesday.