The court’s five justices ruled to proceed behind closed doors, shortly after commencing the hearing against the couple who are suspected of having murdered 20-year-old Abba Rezai in 2005.

The case has been described by lower courts as an “honour” killing as Rezai was in a relationship with the couple’s 16-year-old daughter at the time.

The Supreme Court rarely holds remand hearings, with the last occasion being back in the 1980s. Furthermore it is unusual for the court to order a retrial in a case which implicates another person.

The Supreme Court has ruled to allow a retrial in the case of the couple’s son, who was 18-years-old at the time and who remains the only person convicted in connection to the case.

The man, who is now 23-years-old has completed his four sentence in youth detention and is in the process of appealing a deportation order to Afghanistan.

His parents were meanwhile acquitted despite both the district court and the appeal court ruling that their son could not have committed the crime alone.

Ulf Venderot, one of the investigating officers, told news agency TT that the police suspected at the time that the teenager was not the only person involved in the gruesome killing.

“All of the interrogators believed that son was not telling the whole story, and instead that the whole family was involved. I am not surprised over the retrial,” he said.

In support of his case he has cited the testimony made in police interviews by his younger brother, who was 15-years-old at the time. The teenager spent some time in state care due to concerns over reprisals from his family.

The 22-year-old’s parents however contest the charges and dispute their son’s new version of the events.

20-year-old Abbas Rezai was found dead in an apartment in Högsby in southern Sweden in November 2005.

After a police examination it was concluded that Rezai was scalded with hot oil, hit with a variety of objects and repeatedly stabbed in the back and chest, with the majority of the wounds sustained after his death. He was also almost entirely scalped and one of his fingers had been partially chopped off.

“The victim thought that he had gone to Högsby to be accepted into the family. He was instead fooled into coming to be killed to put an end to his relationship with the daughter,” Ulf Venderot said, adding that the case was his first experience of a so-called “honour killing”.

The issue of “honour killing” gained greater prominence in Sweden following the murder of Fadime Sahindal at the hands of her father in 2002.

Sahindal moved to Sweden as a seven-year-old from Turkey. She leapt to national prominence in the autumn of 2001 when she held a speech in Sweden’s Riksdag telling of her exposed situation at the hands of oppressive male relatives.

She was murdered by her father, Rahmi Sahindal, in January 2002. Sahindal confessed to the crime in police interviews explaining his motive that his daughter had shamed the family by publicising how some Kurdish women were being treated.

The Swedish police estimate that around 1-3 “honour” killings occur each year in Sweden, mostly directed against females.