Intruder jailed for Adelaide sex attack

An intruder who hid in a stranger's bedroom before raping a woman while her boyfriend slept beside her has been jailed for the audacious and bizarre crime.

Mark Lee Duncan, 38, was found guilty in the SA District Court of rape, indecent assault and an aggravated count of serious criminal trespass in February 2012 at Richmond in suburban Adelaide.

Judge Sydney Tilmouth on Thursday jailed him for six-and-a-half years with a non-parole period of four years.

Describing the circumstances as "unusual and puzzling", he said Duncan somehow managed to hide himself in the bedroom in the early hours of morning after entering the house through an unlocked rear sliding door.

Duncan then managed to crawl from the bottom of the bed, along the woman's body, without disturbing either her or her boyfriend.

The rape charge involved his performing oral sex on the woman, who at first had assumed the man was her boyfriend.

The jury was told the boyfriend woke up and saw an unfamiliar man on top of his girlfriend.

After being challenged, Duncan said: "she invited me in, I'm from New Zealand".

Duncan claimed to have no memory of the events, but the jury rejected his defence of having been in a dissociated state and having acted involuntarily.

The judge said the bizarre circumstances of the crime did suggest a person who was not functioning normally.

He said Duncan had a significant impairment of working memory and had suffered from major depression.

Duncan, who spent 10 years with the NZ army, said he had suffered an electric shock while on a tour of duty and on other occasions had lost consciousness.