A US senator today called on the UK to hold an independent inquiry into the release of the Lockerbie bomber, a year after he was returned to Libya.
Abdelbaset al-Megrahi was freed from Greenock prison on August 20 last year after his diagnosis with terminal prostate cancer.
The bomber returned to jubilant scenes in Libya where he remains alive at home, despite being given three months to live at the time of his release.
Senator Robert Menendez said: "We continue to believe that an independent investigation in the UK would provide incredibly valuable new information and we have asked the British and Scottish Governments again to begin that process."
He said he had written to Scottish First Minister Alex Salmond and Prime Minister David Cameron laying out the areas where "questions linger".
There have been several letter exchanges between Washington and the Scottish Government since an announcement by the Senate's Committee on Foreign Relations that it was to hold an inquiry into Megrahi's release.
A hearing was postponed after Scottish Justice Minister Kenny MacAskill and his former UK counterpart Jack Straw declined to attend as witnesses.
The letters sent today by Mr Menendez and fellow senators Frank Lautenberg, Kirsten Gillibrand and Charles Schumer raise questions over Megrahi's medical diagnosis and communications between BP and the British Government.
Speaking in New Jersey, Mr Menendez said: "A mass murderer tasting freedom experiencing joy was a scene that made the stomach turn, that made old wounds fresh again in the hearts of those whose family members died at the hands of this man.
"And although this scene, this entire turn of events was met with anger and frustration in our country and in many other countries around the world, Scottish officials invoked their legal right to take this action allegedly because Mr Al Megrahi had but three months to live.
"Well, here we are one year later. Al Megrahi, a convicted mass murderer, still very much alive, very much free, living in the lap of luxury by all accounts.
"Doctors who examined him while in prison now say he could live for another decade or more.
"And every new piece of evidence builds onto the cloud of suspicion hanging ominously over the circumstances surrounding Al Megrahi's release."
Mr Menendez said: "On this unwelcome milestone, we want it to be known that our desire for answers is as strong as ever, our resolve is deep and our determination will not fade.
"The investigation that I have launched with Senators Lautenberg, Gillibrand, Schumer presses on in search of the truth."
He said that "additional answers and documentation" were needed in regard to meetings between Andrew Fraser, director of health at the Scottish Prison Service, and Libyan officials.
The decision by Mr MacAskill to release Megrahi, the only man convicted of the 1988 Pan Am jet bombing, has also met strong criticism at home.
The UK Government described the decision as a "mistake" and opponents at Holyrood have called for the publication of further medical evidence.
Mr Salmond told the BBC he understood the "anxiety" expressed over Megrahi's release, but his ministers had "followed the due processes of Scots law".
He said Dr Fraser, whose role it was to compile and present a prognosis based on Megrahi's medical notes, had followed a process of "complete integrity".
The First Minister told BBC Radio Scotland's Good Morning Scotland programme: "This is a physician of great experience and I don't think anyone should seriously doubt either his professional or personal integrity."
He said the same procedure has been followed in all 40 cases reviewed in the last 17 years, during which time there had been four cases of people surviving beyond one year.
Mr Salmond also said there was only one medical report on prognosis in existence - the one produced by Dr Fraser.
He added: "Obviously people are going to have a range of views about the rights and wrongs of the decision that we made in the case of Mr Megrahi.
"All we ask people to do is to accept it was a decision that was made in good faith following the due procedures that we have under the legislation and under the tenants of Scots law."
The Foreign Office urged Libyan authorities not to celebrate the anniversary today, saying that any honouring of the day would be "tasteless, offensive and deeply insensitive".
By 5pm UK time there had been no reports of any such celebrations.
A spokesman for Mr Salmond said: "The Senators' latest letter is totally wrong in saying commercial influences played any role whatever in the decision, and is quite misleading - we have published everything we can, and the Senators embarrass themselves by asking us to un-redact material which we are only prevented from publishing because the US government refused permission.
"None of the issues raised in any way alters the fact that the decisions of the Scottish Government were made with total integrity, and according to the due process of Scots Law."
The spokesman said senators had been asked to send public statements they made in June 2007 when details emerged of the Prisoner Transfer Agreement signed by the UK and Libyan Governments.
Megrahi was not excluded from the PTA but the eventual decision to release him was made on compassionate grounds and not on the basis of the PTA.
The spokesman said: "They have sent no such statements, which can only mean that when the Scottish Government was using every means at our disposal to oppose the PTA - including seeking a specific exclusion of anyone connected to the Lockerbie atrocity - there was silence from the Senators."Reuse content