Four U.S. senators who met Tuesday with Prime Minister David Cameron said the British leader could still call for an independent investigation of last year's release by Scotland of a Libyan man convicted in the 1988 Lockerbie bombing that killed 270 people. The senators from New York and New Jersey said Cameron spent 45 minutes discussing the matter with them in a meeting that was added to his schedule the night before. "Our request for an independent investigation was still on the table," said Sen. Charles Schumer of New York. "It was not case-closed." Cameron is in the United States on his first visit as Britain's leader. He met earlier Tuesday with President Barack Obama. Most of the victims in the 1988 bombing of Pan Am Flight 103 were Americans. The flight was headed from Frankfurt, West Germany, to New York via London, England, when it exploded in the air. Abdelbaset Ali Mohmed al Megrahi was convicted in the case and sentenced to life in prison. The Scottish government released al Megrahi on compassionate grounds last August after doctors said he had terminal prostate cancer and just three months to live.