The man who headed the American investigation into the Lockerbie bombing has revealed the case remains open in the US but the political will to pursue those responsible may have been lost.

Former FBI special agent Richard Marquise, who led the US task force on the case which also included the Department of Justice and CIA, said the case is "pending" and investigators still hope new leads will arise.

Abdelbaset Ali Mohmed al Megrahi, convicted of the 1988 bombing that killed 270 people, has begun proceedings for his second appeal.

Mr Megrahi, currently serving a 27-year sentence in Greenock prison, was granted leave to appeal in June following a three-year investigation by the Scottish Criminal Cases Review Commission.

The commission found six grounds of referral suggesting the case could have been a miscarriage of justice, many of which refer to unreliability of the Crown's key witness Tony Gauci, a Maltese shopkeeper who gave evidence about items bought in his shop.

The outline draft grounds of appeal have been lodged with the courts and last week the defence agents demanded the Crown hand over crucial documents that have still not been disclosed to them.

The Herald revealed last week that discussions of financial remuneration had taken place between Tony Gauci, his brother Paul and the CIA.

Mr Marquise, who wrote the book Scotbom: Evidence and the Lockerbie Investigation, also revealed there were discussions between the different agencies about Tony Gauci and whether he or his brother required witness protection.

He said he was unaware of any financial discussions between the CIA and the Gaucis but confirmed the US government ran a rewards programme for information at the time. "I know that when PanAm 103 went down, the State Department had a new programme called rewards for justice," he said.

It was well advertised in the Middle East, but the Scottish legal system has no mechanisms whatsoever for paying people and no comparative witness protection programme.

"We talked about it and we talked about the Gaucis and whether they needed to be protected," said Mr Marquise. "I think someone spoke to them in 1991 and said if you feel threatened we will relocate you, but as far as I am aware no-one offered them millions of dollars. Tony Gauci told someone that Australia would be the only place he might like to go, but he was happy in Malta and did not want to leave his pigeons so the subject was dropped. Instead extra security, including a panic button, was added to his shop."

Mr Marquise, who served for 31 years with the FBI before retiring recently, believes the Libyan was rightly convicted but said members of the Libyan government should have been indicted too.

"There are still people we want to indict from the Libyan government and the case is still pending," he said. "But I don't know there is the political will at the highest level. I don't know that there is a lot of interest in keeping him (Megrahi) in prison. They have made friends with Gaddafi. We knew there were other people to indict but the evidence trail ended.

"I would like to hope that some day we will get the answers, but maybe we will never know."