Mulvihill says double stabbing accidental

Accused murderer Paul Mulvihill says he never meant to kill his former mistress, but a jury has heard his account of her accidental stabbing is a "physical impossibility".

Mulvihill, 46, is accused of stabbing his former lover Rachelle Yeo to death in her North Curl Curl home on Sydney's northern beaches in July 2012.

Mulvihill told a NSW Supreme Court jury that his ex-girlfriend was stabbed by a "massive" kitchen knife during a violent struggle between the two.

He said he never deliberately wounded her, and even re-enacted the stoush with a member of his legal team acting as Ms Yeo, using a ruler to represent the large stainless steel knife that killed her.

But on Thursday crown prosecutor Maria Cinque said everything he did from the moment he went over to Ms Yeo's apartment that night was meant to kill her.

"That is incorrect. I was faced with a very large knife, that had already struck me once," Mulvihill replied.

"I was not going to let that knife hit me again."

"I was defending myself with my body (to) take the knife out of the equation."

But Ms Cinque said it was a "physical impossibility", that Ms Yeo could not have been stabbed twice accidentally the way he described.

"(That) was exactly my recollection of what happened in that unit ... I disagree," he said.

He rejected her suggestion that forensic pathologists said Ms Yeo had been stabbed in the neck first, not the body like he said.

When Ms Cinque said he had in fact stabbed her in the chest "just to make sure she was dead", Mulvihill replied: "Absolutely incorrect".

The court heard earlier Mulvihill had run internet searches of Ms Yeo's Facebook profile and the area of Sydney that he knew she was looking to move to, but he denied he was "obsessed" with her.

Despite recounting the day before how blood poured from Ms Yeo's neck when the blade pierced her, Mulvihill said he thought she was "well and truly alive" when he fled her unit.

"I was shocked when I heard it on the radio in the morning that she was deceased," he said.

The two had an affair while working at Sanofi Aventis pharmaceuticals in Brisbane.

He denied footage of him pacing in and out of Newcastle Airport the morning after Ms Yeo died revealed that he was checking for police.

He said he found Newcastle Airport uncomfortable and was so anxious after the night before he "couldn't sit still".

Mulvihill had decided against taking a scheduled flight from Sydney on that day.

The trial continues, with the jury expected to hear closing submissions early next week.