Clive Carter, a father-of-three, was given a life sentence yesterday after he was found guilty of murdering Khanokporn Satjawat, 42, at the Scottish Exhibition and Conference Centre (SECC) in Glasgow.
The 35-year-old, from Motherwell, North Lanarkshire, smashed Ms Satjawat repeatedly over the head and face with a fire extinguisher in the women's toilets in the Clyde Auditorium in November last year.
He is thought to have flown into a rage because she complained about him checking her security pass.
Every bone on the left side of her face and neck was broken and her skull was shattered into pieces.
Carter admitted killing Ms Satjawat, who had been attending an HIV conference, but denied murder, claiming he had no memory of the incident.
He said the words "die, just die" were in his head as he argued with Miss Satjawat, but he did not say them out loud. "I was angry, frustrated and annoyed," he confessed.
He later went and ate his lunchtime sandwiches.
Jailing Carter, Judge Lord Matthews said: "Khanokporn Satjawat was a hard-working, well-educated and dedicated lady who came to this country to participate in a conference whose purpose was the alleviation of suffering and the saving of lives.
"It is cruelly ironic that, in the course of such an event, the life of that fragile lady should be taken in such a brutal fashion with an instrument whose primary purpose is also the saving of life and the hands of a man to whom she should have been able to look for assistance."
Carter was also convicted of a breach of the peace nine days earlier when he terrified Glasgow hotel guest Stephanie O'Brien, 23.
She did not report it at the time to police and told the trial she was made to feel silly for raising concerns about Carter's behaviour with Holiday Inn staff. Lord Matthews told Carter: "One is left to wonder what the outcome might have been had Ms O'Brien not had the presence of mind to extricate herself from the hotel room before the situation escalated.
"However, your activities that night have understandably left their mark on her."
Lord Matthews told Carter it was up to the parole board to decide when, if ever, he was released. But the security guard must serve at least 20 years before he is eligible for parole.
The jury of eight men and seven women had heard that Carter had major issues with anger management. His wife, Paula, 33, had described "explosive rages" that he could not remember. He once throttled her until she was red in the face. He wrecked their kitchen because he could not find a tin opener.
His GP sent him to counselling, but he quit after two sessions because the counsellor annoyed him.
One of Carter's defence team, solicitor advocate John Paul Moberry, said: "Given the verdict of the jury, there is very little I can say. Mr Carter approached this trial with the position that the death of this lady was caused at his hand.
"There has been evidence before the court of Mr Carter's medical state and there is nothing to add."
Detective Superintendent John McDonald of Police Scotland said: "We sincerely hope this verdict will bring some comfort to the relatives of Ms Satjawat."
His employers G4S, who were not told of the Holiday Inn Express incident, thanked the police, SECC management and their own staff, some of whom were witnesses.
A spokeswoman said: "We would like to pass on our deepest condolences to the family of Ms Satjawat. This was a brutal and unprovoked attack and the sentence passed reflects the severity of the crime."
Holiday Inn Express on Stockwell Street is owned by the Somerston group and operated under a franchise by InterContinental Hotels Group. A spokesman for IHG said: "We have no evidence to suggest that hotel staff behaved other than in an entirely appropriate way in response to the facts."