Six people from Breda twice convicted of murdering the mother of a Chinese restaurant owner in 1993, may not be guilty after all, the advocate general of the Dutch supreme court said on Tuesday.

The advocate general, whose advice is not binding on the supreme court, said there is not enough evidence to convict the six, and that the case should be referred back to the appeal court for a re-think.

It is the second time the supreme court has ordered the case be looked at again. In 2012 the court ordered the case be heard again after new facts emerged about the murder of Tim Mui Cheug, who worked in her son’s Chinese restaurant Peacock in Breda.

The new evidence included an eyewitness who was waiting at a bus stop opposite the restaurant and who heard nothing and traces of blood at the scene which did not come from the victim or the six suspects.

At the original trial in 1994, three men and three women were found guilty of involvement in the murder. The men were jailed for 10 years, the women for two. All deny any involvement in the crime and all have since served their sentences.

The supreme court is due to announce its decision in December.