Jack Straw tonight declined a request to give evidence to a US Senate committee hearing on the release of the Lockerbie bomber.
The former justice secretary said he could not help the inquiry because he had "absolutely nothing to do" with the decision to free Abdelbaset al-Megrahi on compassionate grounds last August.
The refusal came after Scottish Justice Secretary Kenny MacAskill confirmed he would also not be testifying as he had "no information to provide" on alleged lobbying by BP to secure an oil deal with Libya.
In a letter to Senator Robert Menendez, of the foreign relations committee, today, Mr Straw said: "It was, as I understand he has already explained, Mr Kenny MacAskill, the Scottish Justice Secretary who last August made the decision to release Mr al-Megrahi on compassionate, medical grounds.
"I had absolutely nothing to do with that decision. I saw no papers about it, and was not consulted about it.
"Indeed I was on holiday at the time and only learnt about it from an item on the BBC News website.
"I believe that Mr MacAskill has confirmed that the decision was one taken entirely on medical grounds, without involvement from the UK Government, and without pressures from BP.
"It follows from this that I do not see how I could help your committee "understand several questions still lingering from this decision", as I did not make it, nor have any other locus in it.
"You will therefore excuse me if I do not accept your committee's kind invitation."
Mr Straw also insisted that, although he helped negotiate a Prisoner Transfer Agreement between the UK and Libya, that had "no bearing" because it was not used in Megrahi's case.
Members of the US Senate foreign relations committee wanted Mr Straw, Mr MacAskill and BP chief executive Tony Hayward to help them investigate the suspicions of some that oil giant BP may have had a hand in the release of Megrahi.
But this morning, Mr MacAskill insisted that the Scottish Government was "neither party nor privy" to any discussions that may have taken place with BP.
He denied claims that he was "running scared" from an inquiry, and said the Scottish Government was co-operating fully with the US "as best we can".
Mr MacAskill said: "The US Senate's invitation is primarily predicated on an investigation into what may or may not have happened with regard to a BP oil deal.
"The Scottish Government was neither party nor privy to what was going on there, so we've made it quite clear that we have no information that we can provide regarding that.
"If there is any information on points, we are happy to clarify matters but we really can't be of any assistance on that."
He said it was "proper form" for him to give evidence to Holyrood and to Westminster - but not to the US Senate.
He said: "I'm the Cabinet Secretary for Justice. I am accountable to the Scottish Parliament and I'm elected by the Scottish people. That's why when I was asked to appear before a Scottish Parliamentary committee on al-Megrahi, I did so, and that's proper form."
Congressman Eliot Engel, who has campaigned on the case, told BBC Radio 4's PM programme he was "very disppointed" by the decision.
"We just wanted to get to the truth, as everybody on both sides of the ocean.
"It is very troubling that al-Megrahi was released and nobody could understand it. It just doesn't pass the smell test."Reuse content