In a shock twist in one of the Cote d'Azur's most notorious sagas, Guillaume Agnelet, the son of former playboy lawyer Jean-Maurice Agnelet, told a stunned court in Nice that his father had admitted to killing Agnès Le Roux in 1977. This is the third week of the third trial of Mr Agnelet, 76, who has previously been acquitted, sentenced to 20 years in prison and then last year saw the European Court of Human Rights rule there had been a violation of the "principle of a fair trial".

In his retrial on Monday, his second son, who had supported his father in the first two trials, told the court in Rennes, Brittany: "My conscience is weighing on me. After he got out (of the car) and shouted 'help' to see if anyone had heard. Mr Agnelet's youngest son, Thomas, who insists his father is innocent, had been ordered to leave the court during Guillaume's testimony.

I am convinced my father is the killer." Later, he said, his mother, long-separated from Mr Agnelet, had told him: "I'm going to tell you who your father is." "He killed Agnès Le Roux. "He threw the naked body into a river, left the car (a Range Rover) with the keys in the ignition and returned home to Nice by train." Guillaume Agnelet said he had previously kept the information secret to protect his family. Afterwards, he told the judge: "I don't know what is going through my brother's mind." The murder case – a tale of passion, money and betrayal – has gripped the Riviera with its surprise twists and turns since Miss Le Roux, then 29, first went missing 36 years ago.

His father told the court he was "totally stunned" by the allegations. Shortly before her disappearance, Miss Le Roux had fallen out with her mother, who had refused to hand over any inheritance to her unruly daughter.