German neo-Nazis helped the Palestinian terrorist organisation Black September to carry out the infamous massacre of 11 Israeli athletes during the 1972 Munich Olympic Games, intelligence files released nearly four decades after the killings revealed yesterday.

Details from a hitherto secret, 2,000-page document on the massacre, held by Germany's Federal Office for the Protection of the Constitution, were published by Der Spiegel magazine ahead of the 40th anniversary of the Israeli athletes' deaths this September.

Two Israeli sportsmen died in the initial hostage-taking. Nine more were killed during a bungled rescue attempt by German police at Munich airport in which five terrorists were also shot dead.

Israel has been lobbying for a minute's silence to be observed in memory of the massacre at this summer's Olympic Games in London.

Until now it had been assumed that Black September, which some historians claim was linked to the Palestinian Fatah party – bore sole responsibility for the kidnapping and murders which were carried out in an attempt to secure the release of 234 Palestinians held in Israeli jails.

But according to the newly-released German intelligence file, neo-Nazis also helped to prepare the massacre and planned to carry out further terrorist acts in Germany to avenge the police killing of Palestinians in Munich.

The file showed that Abu Daud, the Palestinian behind the massacre, travelled to Germany to plan the attack in July 1972. He was assisted by Willi Pohl, a known German neo-Nazi. It was not clear whether other neo-Nazis were also involved.

The documents cited police in Dortmund who kept Daud under surveillance. They said he met Pohl several times and that the neo-Nazi boasted to his employers about his contacts with a radical wing of the Palestine Liberation Organisation.

Der Spiegel said the police report was widely circulated, but there was no evidence the intelligence services made any attempt to find or arrest Daud. The Palestinian was apparently able to prepare his plan to attack the Munich Olympic village undetected, the magazine reported.

The files revealed that Pohl put Daud in touch with an expert in counterfeiting passports and other official documents, and acted as his personal chauffeur. Pohl, who has since renounced terrorism and neo-Nazi activity, is now a crime writer who has assumed a new name. He told Der Spiegel: "I drove Abu Daud all over Germany and he held meetings with Palestinians in various cities."

He claimed he was linked to the Munich massacre "without knowing it".

The documents showed Pohl was later involved in a plan by Palestinian activists to carry out a series of kidnappings at Cologne cathedral and town halls across Germany, which were meant to avenge the deaths of Palestinians shot dead by police after the Munich massacre. Pohl was ordered to carry out the attacks by Abu Jihad, then the deputy of PLO leader Yasser Arafat. But he was arrested in Munich in October 1972.