It was the kind of phone call every mother dreads. At 4.24am on 27 March 2003, Erica Duggan was woken by her son Jeremiah, a normally ebullient 22-year-old. "Mum, I'm in trouble," he said. In hushed tones, he told her he was in Germany and began spelling the letters of the place he was staying, "W, i, e, s ...". Then the line went dead.

The next call came from the police. German officers had found Jerry's body three hours later on the side of the B455, a busy dual carriageway running south-east out of the city of Wiesbaden towards the Rhine. Witnesses said a man had scrambled into the centre of the road and was hit by a brown Peugeot 406, and then a blue Volkswagen. By the time paramedics and police arrived, Jerry was dead of head injuries.

The subsequent police investigation was perfunctory, classifying his death as a suicide. Witnesses were allowed to leave the scene, cars were moved before being photographed and an external post-mortem was conducted at a nearby mortuary without any detailed forensic checks.

Few parents would find it easy to accept that their child has committed suicide but for Mrs Duggan, a retired teacher from north London whose Jewish family fled the Nazis in the late 1930s, the idea that her son took his life did not make sense.

"He had so many plans for the future and never showed even the slightest inkling of depression," she told The Independent, in her mother's home in Golders Green. "But it's more than just that. The call I got from him just before he died, that was from someone who desperately wanted to live, who was trying to survive. It wasn't from someone intent on killing himself."

Mrs Duggan, in deep doubt of the German police belief that her son's death was suicide, hired private investigators and forensic experts to look at the evidence again, eventually selling her house to pay the costs and moving in with her ageing mother. Their reports have cast serious question marks over the official portrayal of Jerry as suicidal, suggesting instead a man who was either desperately trying to escape unknown assailants when he stumbled out on the dual carriageway, or who had been attacked before he got there.

Yesterday, armed with this new evidence, the Duggan family's lawyers went to the High Court after the Attorney General, Baroness Scotland, took the highly unusual step of granting them permission to seek a second inquest into Jerry's death.

The first inquest, in 2004, rejected the German police suicide suggestion, and returned an open verdict, finding instead that he had died in a "state of terror". But investigators failed to look wider. Supporters hope a fresh inquest will finally force German police to reinvestigate why a British Jew died in mysterious circumstances after spending five days with a far-right political cult led by a convicted fraudster who is known for his virulent anti-Semitic views.

Jerry had been a student at the British Institute in Paris but he had travelled to Wiesbaden to attend what he thought would be an anti-Iraq war conference. "He was an idealistic boy who wanted to change the world," his mother said. "He was angry about the upcoming war and wanted to do something about it. But he was also excited because he was beginning to learn about politics."

The conference was organised by the Schiller Institute, an extremist political think-tank linked to a right-wing conspiracy theorist, Lyndon LaRouche. He is an 87-year-old convicted fraudster who has made eight unsuccessful attempts to run as an independent candidate in the US presidential elections. Some of LaRouche's more unusual claims include that the British monarchy and MI6 are behind the global drugs trade.

In the States, he is largely regarded as an amusing sideshow whose apocalyptic writings attract vulnerable people looking for answers. But underlying much of his work is a deep anti-Semitism that describes the world as being controlled by a mass Zionist conspiracy of bankers, lobbyists and politicians.

The Schiller Institute, run by his German-born wife, spreads that message around Europe; on the night Jerry died, LaRouche addressed the conference in Wiesbaden. In Jerry's notes on the five days he spent there, Mrs Duggan discovered that her son had become aware of the anti-Semitic agenda of many LaRouche followers and had spoken out against them. "There were a lot of comments blaming the Jews for Iraq and he got up to say that he was Jewish and he didn't support the war," she said. "Whatever happened it's clear he fell out with these people very quickly."

La Rouche blames the CIA, MI6 and the KGB for any political or media criticism aimed in his direction. He described the Duggan case as a hoax contrived by "admirers of [former US Vice-President] Dick Cheney and Tony Blair". Mrs Duggan's efforts to investigate her son's death is, he says, a "smear".

Paul Canning, a former Scotland Yard forensic officer, has studied the 79 photographs taken by German investigators of the crash site and Jerry's body. German police said he was hit by the Peugeot, then run over by the Volkswagen. But Mr Canning could not find evidence of tyre marks on the body. Nor was there any blood, flesh or hair on either car.

Mr Canning, who has investigated hundreds of road fatalities, believes this is "inconceivable", reporting that he had never come across a high-speed collision of a car and pedestrian where no traces of blood are found. "I do not believe the images depict how Jerry came to meet his premature death," he added. "It is possible that Jerry lost his life elsewhere, prior to being placed at the scene."

Terence Merston, another former Met Police investigator who has studied the photographs, backs Mr Canning. "Based on my years of experience in attending thousands of crime scenes as a forensic scene examiner, it is my opinion that the evidence at the scene points towards Jeremiah's death being extremely suspicious and not a road traffic accident," he said. "It is also my view that the damage to the Peugeot car has been deliberately caused."

But how did Jerry sustain the head injuries that killed him? A post-mortem by a British pathologist, Dr David Shove, discovered defence wounds on Jerry's arms as well as blood in his lungs and stomach. At the speed that witnesses say he was struck, he would have been killed instantly, but the blood in his lungs and stomach (caused by breathing in and swallowing after a major haemorrhage) suggest he was alive for some time, after intense trauma.

Mrs Duggan said: "What we really need is for Germany to look again at my son's death." But the German authorities are reluctant to act. A bid by German lawyers claiming police breached human rights laws by failing to investigate properly has floundered for four years in the country's highest court, the Federal Constitutional Court. Police in Wiesbaden have refused to reinvestigate, or reopen their files.

Now, a British inquest is the best opportunity the Duggan family has for finding out what really happened to Jerry. "It's been a long and difficult journey but I'm beginning to think we may be nearing the end," a visibly exhausted Mrs Duggan added. "From the moment I got that call it's been a seven-year fight for justice. I can't stop now."

The LaRouche Movement: A 'sinister' cult

*Described in an internal Scotland Yard memo as a "political cult with sinister and dangerous connections", the LaRouche Movement is an international party of activists who follow the writings of its American founder, Lyndon LaRouche, above.

*Now 87 years old, LaRouche began his career in politics as a fervent Marxist living in New York in the 1970s. He then performed a political U-turn to become one of America's most unconventional and populist far-right conspiracy theorists.

*In his writings, a mass conspiracy led by Britain, Russia, the US government and the world's Jews is described as the major cause of global problems.

*He has run as an independent candidate in every US presidential election since 1976 – apart from in the early 1990s when he was convicted for fraud conspiracy and tax evasion.

*Because Britain, and in particular the monarchy, is regarded as the arch-imperialist enemy, the movement has made little headway in the UK.

*LaRouche activists have, however, made inroads at European universities through the Schiller Institute, a Wiesbaden-based think-tank which was founded by LaRouche's German-born wife and regularly features his writings and speeches.