Four U.S. senators are calling on Britain to investigate the circumstances of last year's release of the man convicted of the Lockerbie airliner bombing. Abdel Baset al-Megrahi was released from a Scottish prison in September because a doctor said the cancer-stricken man had only three months to live. However, the doctor later said al-Megrahi could live for another decade. Al-Megrahi had served eight years of a life sentence for the Dec. 21, 1988, bombing of the Pan Am Flight 103 as it flew from London to New York. Democrats Kirsten Gillibrand and Charles Schumer of New York and Frank Lautenberg and Robert Menendez of New Jersey requested the investigation Wednesday in a letter to the UK's ambassador to the U.S.