Clive Carter, 35, from Motherwell, denies murdering Khanokporn Satjawat at the Clyde Auditorium, Glasgow, on November 12, last year.
The security guard has admitted killing her but claims diminished responsibility and says he has no memory of the attack.
Carter, who was in the witness box at the High Court in Glasgow yesterday giving evid-ence for a second day, denied orchestrating a cover-up after the killing.
He told John Scullion, prosecuting: "I don't remember destroying the evidence."
He has admitted smashing 42-year-old Miss Satjawat, from Thailand, over the head and face with the extinguisher smashing her skull and most of the bones in her face. She was in Glasgow attending an HIV conference.
The brutal attack took place in the ladies' toilets on the second floor of the Clyde Auditorium.
Carter claims he has no memory of the killing. He said he remembered arguing with his victim and the next thing he recalled was eating his sandwiches for lunch minutes later.
Mr Scullion asked Carter: "Did you tell a psychiatrist that you have always known that you were responsible for the killing of Khanokporn Satjawat?"
He replied: "I was looking back on things. At the time of the incident I wasn't fully aware, it was only after having time to reflect."
Carter also told the jury he had no memory of washing blood from the fire extinguisher and then hiding it in a room in the complex.
Mr Scullion said: "You took the fire extinguisher down from the second floor to room 136 and the purpose for that was to clean it of blood. Carter replied: "I don't remember."
He also denied hiding his bloodstained G4S blazer.
The trial continues.