Since his capture, Vinas has been talkative and cooperative, providing a detailed account of his sojourn and testimony for upcoming terrorism trials in Europe, the officials said.

In March, he gave a statement in New York to a magistrate and police from Belgium that will be used as evidence against three jailed Belgians who admitted to training with Al Qaeda. He also has been questioned by French investigators.

Vinas told investigators he arrived at the camps in December 2007, anti-terrorism officials said. Despite Al Qaeda's fear of spies, Vinas was treated well because someone in the network's structure had vouched for him.

'He had a good reference, so they trusted him,' an anti-terrorism official said.

Vinas admitted to meeting front-line chiefs of Al Qaeda operations to discuss his training and potential role in the network, officials said.

In conversations between March and November 2008, Vinas gave the leaders 'expert advice... derived from specialised knowledge of the New York transit system and Long Island Railroad, communications equipment and personnel, including himself', according to court papers opened Wednesday.

A lawyer for Vinas would not discuss the charges against him or his cooperation with the authorities in the US or Europe. 'We would just ask the public to withhold judgment until all the facts come out in this case,' the lawyer, Len H. Kamdang, told the New York Times.