The public prosecutor's office in Graz said that the body was found wrapped in a plastic bag, buried near the Austrian border in Szentgotthard-Rabafüzes.

An autopsy will be carried out on Wednesday to confirm that it is the missing 16-year-old Marcel S from Carinthia.

Meanwhile more details are starting to emerge about the 16-year-old boy, Sebastian S, who was arrested after Marcel’s murder in a middle-class area of Graz.

His mother, Gabi S, has spoken to the Heute newspaper and said that a few hours after the shooting her son and her father turned up in Bad Vöslau (Lower Austria), where she was having a spa holiday. “My boy stood before me, howling and trembling all over,” she said.

She said that he confessed to the crime – and told her that he had shot his friend Marcel after he tried to force him, at gunpoint, to rape a 14-year-old girl whom they had invited over.

“This is a huge nightmare for me,” Gabi said. “I think my son was drugged – he is not a murderer.”

However, parents who sent their children to a Kindergarten which Gabi ran in Graz say that official complaints were made about Sebastian’s behaviour when he was younger.

Sebastian and his grandfather are both in custody.