The Board of Deputies has criticised the German Chancellor Angela Merkel for ignoring a letter requesting an independent investigation into the death of Jeremiah Duggan.
Mr Duggan was 22 when he was found dead on the roadside in the town of Wiesbaden in 2003 after attending a youth event organised by Larouche, widely regarded as a cult-like group.
The original police investigation concluded his death was suicide, but the verdict has always been disputed by the Duggan family. His mother, Erica Duggan, claimed that German police destroyed evidence and carried out a cover-up.
In a letter sent in December, Board president Vivian Wineman urged Mrs Merkel to look into what had happened. He said he was "most disappointed" by her failure to reply. He said: "In addition to the enormous anguish caused to Mrs Duggan, the case raises some very serious issues."
In the letter, Mr Wineman questioned the the conduct of German police and pointed out that a coroner's investigation had been reopened in the UK.
Mrs Duggan also expressed frustration that a letter she wrote to Mrs Merkel had also been ignored. "This, in a country that says they want to fight antisemitism," she said.
The German embassy did not respond to a request for comment.