Hilary Bonnell could have been alive when she was buried, a pathologist testified at the first-degree murder trial of Curtis Bonnell on Monday.

Dr. Ken Obenson, who performed the autopsy on the 16-year-old's body, told the Miramichi courtroom the probable cause of death was asphyxia.

That could have been caused by someone covering her mouth, or by her choking on something, he said, adding that he believes the manner of death was homicide.

Curtis Bonnell, 32, of the Esgenoopetitj First Nation, is charged with first-degree murder in the death of Hilary.

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Hilary Bonnell disappeared from her northern New Brunswick community in September 2009. (RCMP)

The Crown alleges Bonnell picked up Hilary on Sept. 5, 2009, as she was walking along Micmac Road in the province's northeastern community after a party.

He is accused of holding Hilary against her will, sexually assaulting her and killing her.

Last week, the jury watched a police video, where Bonnell admitted he killed Hilary in his backyard after they had sex.

Bonnell told police they fought because she wanted $100 in exchange for the sex and he refused. He said he covered her mouth to stop her from yelling and the next thing he knew, she was dead.

Obenson testified he was unable to determine the exact cause of death during the Nov. 14, 2009 autopsy.

He did not find any fractures or injuries other than two cuts — one on her head and one near her eyebrow, he said.

He did not find any foreign DNA that could indicate a sexual assault either, he said.

Under cross-examination, the pathologist said there was cannabis in Bonnell's system. There was also evidence of alcohol in her system, but there was no indication of how much.

Hilary's body was located in an isolated wooded area near Tabusintac about two months after she went missing.

Bonnell led police to the burial site, the court has heard.

The trial started on Sept. 17.