A man who killed his ex-partner by repeatedly stabbing her at a Perth court complex has been found guilty of murdering the mother-of-two.

Paul Gary Turner, 43, smuggled a knife into a pre-trial conference with Sarah Marie Thomas at Joondalup Justice Complex in December 2016 and stabbed her six times, including three times in the neck.

One of the stabs severed the 33-year-old's carotid artery, which killed her within seconds.

Turner was captured on CCTV footage sitting in the waiting room outside the meeting before the attack, peering into a lever arch folder.

Paul Gary Turner, 43, smuggled a knife into a pre-trial conference with Sarah Marie Thomas at Joondalup Justice Complex in December 2016. (9News)

Prosecutor James Mactaggart says he either hid the knife in there or in his pocket.

About four minutes into the meeting, the registrar ran out of the room before Turner emerged and slid against a wall to the floor, where he sat until detectives and security guards rushed over to arrest him.

At his Supreme Court of WA trial, he wept as he claimed the last thing he recalled on the morning of the killing was speaking with their children.

Turner said his next memory was being in a police station with blood on his hands.

He insisted that after he had an accident while working as a truck driver in 2015, he suffered symptoms including seizures that caused blackouts, sometimes lasting more than 45 minutes.

Mr Mactaggart dismissed Turner's claims as "a pack of absolute lies", saying he was fully aware of what he was doing, and had spent more than 100 hours getting neurological tests but his results kept coming back normal.

He was humiliated Ms Thomas had got the better of him in a bitter custody dispute, obtaining a court order to recover the children days earlier, and she refused to settle with him at the meeting over his claim she owed him money, the prosecutor said.

Defence counsel Lisa Boston argued her client had experienced insane automatism, telling the jury in her closing address that it would have been "bonkers" for a man trained in military knife techniques to knowingly kill someone in a complex packed with security guards and police.

Turner trained in artery-slashing commando techniques and knife concealment when he was aged in his late 20s and continued to practice during his eight-year relationship with Ms Thomas.

Asked about this interest, Turner replied it was "for the historic aspect" as he studied the Fairbairn system used in WWII.

Turner will face a sentencing hearing on October 15.

Mr Mactaggart described the crime as an "outrageous act of evil".