The Senate Foreign Relations Committee will hold a long-awaited hearing Wednesday that aims to find out why Scotland last year gave a controversial "compassionate release" to cancer-stricken Lockerbie bomber Abdel Baset al-Megrahi.

But the session may only widen the gulf between U.S. politicians demanding a more detailed medical explanation of how Megrahi won his freedom and Scottish officials who are declining to provide one.

A Senate staffer's fact-finding trip to Britain this month appears to have produced even more conflict between the U.S. and Scotland, particularly surrounding the details of Megrahi's prognosis and the question of whether he began chemotherapy treatments before or after he was released by the Scots.

The Senate staffer met with George Burgess, who was Scotland's deputy director for Criminal Law and Licensing at the time of Megrahi's release. According to an aide to Sen. Robert Menendez, (D., N.J.), the senator who is heading the hearing, Burgess said the convicted bomber began chemotherapy before leaving Scotland. According to the aide, the Scottish official also said it was Peter Kay, Megrahi's general practitioner in the Scottish prison system, who issued the prognosis that Megrahi had about three months to live—a guideline prisoners must meet to qualify for compassionate release in Scotland. That prognosis was later sanctioned by Scottish Prison Service medical administrator Andrew Fraser. The hearing stands to address both those assertions on Wednesday, the aide said.

Scotland, however, says that isn't an accurate portrayal of what was said in the meeting. Mr. Burgess couldn't be reached to comment.

"It is a matter of public record that Megrahi was not on chemotherapy treatment in Scotland at any point," a spokeswoman for the Scottish government said in an email Tuesday. She added that "the responsibility to provide a reasonable estimate of prognosis was Dr. Fraser's—no one else's—and therefore the prognosis was his." The spokeswoman didn't say whether Dr. Kay agreed to the prognosis, or made it initially.

Megrahi is the only person convicted for the December 1988 bombing of Pan Am Flight 103 that killed 270 people, including 189 Americans, when it exploded over Lockerbie, Scotland. On Aug. 20, 2009, Scotland granted him a so-called compassionate release on the grounds that the Libyan convict, suffering from terminal prostate cancer, had about three months to live.

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