Tony Halloun, a western Sydney concreter, is on trial for the murder of Shahnaz Qidwai, 65, whose body was found in the main bedroom of her three-storey waterfront home at Henley by one of her four adult children on the afternoon of June 15, 2012.

The Crown alleges that Mr Halloun's business, Totalcrete, was in the red to the tune of $97,000 and that he robbed and then killed Mrs Qidwai after she and her doctor husband had employed him to concrete their driveway and build several retaining walls.

The court heard that, during his first interview with police, Mr Halloun denied killing the grandmother, stating that he had "never, never walked into the house".

However, when the tradesman subsequently learnt that police were planning to take a DNA sample and had already spoken to his concreting assistant, who was present at the time, he contacted officers and told them he had "more to say".

After giving police a four-page written statement, which he declared was "200 per cent correct", he told them that he now remembered Mrs Qidwai inviting him inside and that she had given him a hug and put her head against his, and that this was probably how the DNA had been exchanged.

Police did not accept this explanation, charging Mr Halloun with murder soon after.

The court heard that, a year later, having examined the evidence against him, Mr Halloun contacted police again and said he had "more information".

In this interview, he allegedly claimed that, while he was inside the house, three intruders had burst through the door brandishing handguns.

He claimed that the men were dressed identically in black jumpers, tracksuit pants and shoes, with matching black and white baseball caps.

"Mr Halloun told police all were aged 20 to 25, all had black eyebrows and all sounded as though they were born overseas but had spent time in Australia," Crown prosecutor Giles Tabuteau told the jury on Tuesday.

He claimed the intruders, who allegedly referred to each other by their first names – Gus, Moey and Omar – had ordered him to drag Mrs Qidwai into another room.

This, he allegedly suggested, was how his DNA came to be on her body.

He said the intruders had said "we know where you live, we're not here for you, we know you have got a wife" and that if he told the police they would be killed.

The concreter said that he saw Mrs Qidwai was danger but, under threat from the intruders, he allegedly put his steel-capped boots on, went outside to the ute and had a cigarette.

"It is the Crown case that the whole scenario of Gus, Moey and Omar was a complete fabrication and that he was the attacker," Mr Tabuteau said.

Mr Halloun's offsider on the job never saw the intruders arrive and, despite conducting a state-wide search, police never found the type of blue utility Mr Halloun said they had been driving.

Foot impressions consistent with the accused were found moving in a circle downstairs and heading up to the main bedroom.

Police also obtained text messages the concreter sent to his offsider in which he said "don’t say anything until I speak to .. please, anyone" and "I didn't go into the doctor's house".

Mr Halloun's defence barrister, Peter Lang, accepted that there were "inconsistencies" between his client's three police interviews but urged the jury to "keep an open mind".

He said that DNA evidence often raised "as many questions as it answered" and asked how $3420 – the amount stolen from the house – could amount to a motive for murder.

The trial continues.