The Scottish government has denied it had any contact with oil giant BP before its decision last year to release the Libyan man convicted of the 1988 Lockerbie bombing.
It said instead that former intelligence officer Abdel Basset al-Megrahi was released on compassionate grounds, as he had terminal cancer and only three months to live.
The US Senate plans to ask BP officials to testify over their lobbying links with Libya.
al-Megrahi was the only person convicted of the bombing of Pan Am flight 103 over Lockerbie in Scotland in 1988, in which 270 people, mostly Americans, died.
He was sentenced to life imprisonment in 2001.