Goodwood's Marco Daniel Rusterholz, 49, has pleaded not guilty to killing Joshua Newman and Angela Hallam at her Pioneer Parade home on August 15 last year.

South Australian man David Ronald Morgan, 55, who has pleaded not guilty to conspiring to murder Ms Hallam, appeared alongside Mr Rusterholz yesterday.

Crown witness Elisa Knight told the court that both accused came to her Brooker Highway home, where a party was taking place, after the alleged murders took place.

In a police statement she said Mr Rusterholz told her about a month after Mr Newman's death that he felt sorry for him because the 21-year-old "was in the wrong place at the wrong time".

She also said her partner at the time had "bragged" multiple times about killing Ms Hallam because Mr Rusterholz "didn't have the balls" but that he was a compulsive liar and drug user.

Tasmania Police Detective Inspector David Plumpton told the court he had spoken to this man, who he had charged with murder once before in an unrelated matter, but did not figure him as being behind Ms Hallam's death.

Inspector Plumpton said he later received a letter from Mr Rusterholz, at this stage on remand in Risdon Prison, blaming the other man for the murder and castigating police for not doing "a very good job".

The officer said he'd spoken to a bikie who told of burning evidence with Mr Rusterholz.

He described the people involved in the incident as "exaggerators and liars".

Tasmania Fire Service senior station officer Craig Maxwell attended Ms Hallam's apartment to investigate the fire that occurred there the night of her and Mr Newman's deaths.

Mr Maxwell said sections of carpet taken from underneath the couple's bodies tested positive to a fire accelerant. In his report he said petrol had been splashed or poured inside the home.

The fire was deemed to have been deliberately lit.

Forensic scientist Corey Griffiths said a red fuel can, found in a garage at Rocherlea, contained a 1-in-100 billion DNA match with Mr Rusterholz.

The can also contained 1-in-100 billion DNA matches with Mr Morgan and Mr Newman.

The proceedings in front of magistrate Tim Hill resume today.