Both then Walcha Sergeant Anthony Smith and forensic officer Sharon Parsons gave evidence on Wednesday in the NSW Supreme Court trial against murder-accused Natasha Beth Darcy.

When Sergeant Smith arrived at the property Pandora in the early hours of the morning on August 2, the flashing blue lights of an emergency vehicle were the first sign that there had been a serious incident at the normally quiet country property.

Speaking with Darcy's estranged husband Colin Crossman, one of the town's only paramedics, Sergeant Smith was told Mathew had killed himself and that Darcy had found him with a bag on his head.

Mr Crossman had received a text message from Mr Dunbar's phone an hour before he died that said: "Tell the police to come, I don't want Tash or the kids to find me".

The jury heard Darcy told Sergeant Smith that Mr Dunbar had picked up the helium bottle used to gas him at a place near the airport in Tamworth and had told her "it was for welding".

In the hours after Sergeant Smith attended the scene, Forensic Services Unit Senior Constable Sharon Parsons arrived to meticulously search the family home.

The jury heard how Senior Constable Parsons used a "layered onion" approach to go through bins in the home, taking a photo of each layer as she removed items including a Golden Circle Sunshine Punch juice bottle, a bottle of Clonidine and a blister pack of Nexazole.

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She told the court a wine glass was swabbed, vomit found on the bed was tested and a piece of the carpet had to be removed and sent off for analysis due to a stain behind the deceased's head.

Darcy has pleaded not guilty to the murder charge but she has admitted to aiding and abetting suicide - something rejected by the Crown.

She is accused of sedating and gassing Mr Dunbar on the night of August 1.

The trial continues on Thursday.

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