(CNN) -- Doctors for convicted Lockerbie bomber Abdelbaset Ali Mohmed al Megrahi had no role in the decision to release him last year on compassionate grounds because of prostate cancer, according to information from Scotland authorities Tuesday.
Three doctors hired by Libyan authorities to assess al Megrahi "played no part of any kind in the decision on compassionate release," according to the information provided on background by a Scottish government official.
Al Megrahi was given three months to live when he was set free by Scotland last year to return home to Libya.
He is still alive today, and four U.S. senators from New York and New Jersey are demanding answers from Scotland on details of the decision to release him.
Al Megrahi was convicted in the 1988 bombing of a Pan Am jet over Lockerbie, Scotland, that killed 270 people -- most of them Americans. He was serving a life sentence when released in August 2009.
In a letter Tuesday, the four Democratic senators -- Robert Menendez and Frank Lautenberg of New Jersey, and Charles Schumer and Kirsten Gillibrand of New York -- asked the Scottish government to release al Megrahi's full medical records.
"We understand that an extensive medical record was used as the basis of the decision to release Mr. al Megrahi, but only one three-page medical document with redactions has been released by the Scottish government," wrote the senators. "Independent examination of Mr. al Megrahi's complete medical record is necessary in order to understand the circumstances surrounding his compassionate release."
A Scottish government spokesman told CNN on Tuesday that the senators' letter had been received, and there would be a response in due course.
Additional information provided on background concluded that a three-month prognosis for al Megrahi was a reasonable estimate, said Dr. Andrew Fraser, the director of health and care of the Scottish Prison Service.
Fraser's assessment was the medical report submitted to the justice secretary, along with reports from the Parole Board and the prison governor, according to the information, which also said all the reports supported a compassionate release of al Megrahi.
It said Fraser relied on advice from various cancer specialists and denied media reports that the decision was based on the opinion of one doctor.
According to the information, the assessments by the three doctors hired by Libya -- identified as Ibrahim Sherif, Karol Sikora and Jonathan Waxman -- were never considered by Fraser.
The U.S. senators have repeatedly voiced suspicions that Scottish authorities released al Megrahi as part of a deal allowing oil giant BP to drill off the Libyan coast. BP, a British corporation, is already dealing with a public relations nightmare as the company responsible for the Gulf of Mexico oil disaster.
Menendez plans to hold a Senate Foreign Relations Committee hearing on the controversy surrounding al Megrahi's release. His first attempt was postponed after several British officials declined invitations to testify.
Menendez accuses the Scottish and British governments of trying to point the finger of blame at each other in the decision to release al Megrahi.
The four senators met for 45 minutes with Prime Minister David Cameron last month and asked the British leader for an independent investigation into the release of al Megrahi.
CNN's Talia Kayali and Shawn Nottingham contributed to this report