Police have arrested the identical twin brother of Stephanie Scott's alleged killer Vincent Stanford in relation to the NSW teacher's murder.

Officers arrested 24-year-old Marcus Stanford at his home in Forreston, South Australia, this morning as part of the investigation into the murder of the Leeton school teacher.

Marcus Stanford faced Mount Barker Magistrates Court where NSW Police sought his extradition.

Facing the magistrate, Stanford was asked if there was any reason his extradition to NSW should not be allowed.

"I've never been there so I wouldn't need to return," Stanford replied.

The magistrate approved the extradition to NSW.

SA Police said Stanford, who works at a flower farm, would remain in their custody until 7:00am on Thursday whereupon he would be released into the custody of two detectives from NSW.

They expect him to fly out of South Australia about 9:30am and he will be delivered to the Central Local Court in Sydney.

Once in NSW, police say he will be charged with being an accessory after the fact.

Ms Scott was last seen at Leeton High School about 11:00am on Easter Sunday - just days before her wedding.

Vincent Stanford was arrested and charged with her murder four days after her disappearance.

Marcus Stanford will be extradited to NSW where he is expected to be charged with being an accessory after the fact. ( ABC News )

The next day, on April 10, her burnt body was found by police in the Cocoparra National Park about 70 kilometres from the town of Leeton.

Last week when Vincent Stanford appeared before Griffith Local Court, he was charged with the aggravated sexual assault of the 26-year-old before her death.

He was also charged with inflicting actual bodily harm.

The Griffith Local Court was told there was so much evidence involved in the case, a three-month adjournment was needed for it to be forensically analysed.

Vincent Stanford was a cleaner at Leeton High School in the NSW Riverina region where Ms Scott worked.