"I killed her."
Clive Carter, from Motherwell, North Lanarkshire, said he had no memory of battering Khanokporm Satjawat to death with a fire extinguisher in the women's toilets in the Clyde Auditorium on November 12 last year.
However, he said that after talking about the incident with psychiatrists and psychologists he remembered hearing the words "Die, just die" in his head.
Ms Satjawat was bludgeoned on the left side of her head with a fire extinguisher as she lay prone in a cubicle in the ladies' toilets. The force of the assault shattered all the bones on the left side of her face and smashed her skull.
The 42-year-old Thai national was in Glasgow to attend an HIV conference at the SECC.
Carter, 35, said all he could remember was having a verbal argument with Ms Satjawat about her security pass and then sitting in the staff rest room afterwards eating his sandwiches.
In evidence at the High Court in Glasgow the father-of-three told defence QC Ian Duguid he had a row with her when she asked why she should show her security pass.
Mr Duguid said: "Your emotions at the time were that she should just die, is that correct?" Mr Carter replied: "Yes."
Carter said that after arguing for a couple of minutes Ms Satjawat pulled out her pass and waved it in his face.
After killing her he went on his lunch break and was in the rest room when a colleague said there had been an incident in the toilets.
Carter said when he went up he saw Ms Satjawat lying dead in a cubicle.
He denied he had tried to cover up what he had done by hiding his bloodstained blazer and trying to wash blood off the extinguisher.
He was asked by Mr Duguid: "You accept you are responsible for the death of this lady. How do you feel about that?" He replied: "I hate myself. I struggle to understand and explain what happened. It doesn't make sense to me."
Carter was asked if he could think of a reason for what he did and said: "No, not really. I know we had an argument, but that was no reason to do what I did."
The court heard Carter had been prescribed anti-depressants by his GP, but was not taking them. He has also been attending anger management counselling.
Carter told the trial he has smashed kitchen equipment, a TV, a window and a computer during rages at home. He said: "It's like my head being squeezed, pressure and then me exploding. Afterwards I'm calm, everything is mellowed. There's no anger left." Carter said he could never remember the incidents.
He also admitted to having struck his wife Paula during disputes and said the police were often at their door, though he has no convictions for assaulting her.
Under cross-examination by advocate depute John Scullion, prosecuting, Carter admitted he had been up on level two of the Auditorium for 10 minutes before he encountered his victim.
Mr Scullion said: "You were having a skive. You were hanging around in the area for no good reason." Carter replied: "Yes."
Carter admits killing Ms Satjawat but denies murdering her, claiming diminished responsibility.
He claims he was tired because of the shifts he was working with security firm G4S and said he had only had two and a half hours' sleep before heading for his shift on the day of the killing.
The trial continues.