Video shows moments before father allegedly stabs his ex-wife to death during a courthouse mediation meeting

Turner being led away after the attack. Photo / Supplied

A court in Western Australia has heard how a man allegedly used "commando knife skills" to kill his ex-wife as they met in mediation at a courthouse.

Paul Gary Turner, 43, is appearing in Western Australia's Supreme Court, charged with the murder of his ex-wife Sarah Marie Thomas in December 2016.

The prosecution alleges that the father of two brought the knife to the mediation session, held at Joondalup court complex, and then "deliberately, consciously and intentionally" stabbed her multiple times.

Senior state prosecutor James Mactaggart told the court that Turner requested the conference, ostensibly to discuss money he claimed he was owed, and smuggled in a sharp knife that could be found in any "suburban kitchen".

Mactaggart said that moments after the court registrar, who had mediated the session, left the room Turner attacked his ex-wife, stabbing her six times - including a blow to her carotid artery that was described in court as "unsurvivable".

CCTV footage shows Turner repeatedly putting his hands in his pockets as he waits for the meeting to start before heading into the room followed by Thomas.

Five minutes later the registrar rushes out, followed by Turner who sits down before being arrested by police.

Sarah Marie Thomas was murdered at the Joondalup Justice Complex. Photo / Supplied

The court heard that Turner received martial arts training a decade earlier, including in the use of "commando knife skills" to inflict fatal injuries.

Turner's lawyer admitted that her client has trained in techniques popularised by British paratrooper WE Fairbairn.

Pathologist Clive Trevor Cooke told the court that Thomas was stabbed through her left ear, with the knife hitting her skull and damaging the surface of her brain.

"That requires a fair bit of force," Cooke said.

He added that the wound to her neck that severed her carotid artery would have caused "torrential, immediate" and unsurvivable blood loss.

Turner has pleaded not guilty to the murder charge.