Rohen James Hanson is on trial for the murder of his then-partner Dee Annear during a camping trip in September 2021.
The pair drove from their home in Wingham, near Taree, to the Bulga State Forest on the NSW mid-north coast, where they planned to spend four nights.
The holiday turned violent and Ms Annear was killed either on the evening of September 17 or the following morning, crown prosecutor Carl Young said as the NSW Supreme Court trial started on Wednesday.
Hanson assaulted his partner, resulting in "particularly serious injuries" to her head and skull, which ultimately caused her death, Mr Young told a Coffs Harbour courtroom.
"Mr Hanson acted at that time with the intention to either kill or cause very serious harm to Ms Annear," he said.
Standing in the dock wearing a suit and tie, the 41-year-old man pleaded not guilty to murder but guilty to manslaughter.
His plea to the lesser charge was not accepted by prosecutors.
Mr Young told jurors the evidence was expected to show instances of domestic violence allegedly perpetuated by both Hanson and his then-partner.
"This was quite a volatile relationship in which arguments and fights happened with some frequency," he said.
There would also be evidence that the couple abused alcohol and drugs, he said.
Justice Peter Hamill warned jurors they would see distressing and confronting evidence.
The trial, which is expected to last three to four weeks, continues.
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