Washington (CNN) -- 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.
Al Megrahi is still alive, and news reports in recent days have questioned whether he was as sick as depicted. Questions also have been raised about whether a deal was cut to release him to protect British business interests in Libya, possibly involving oil giant BP.
Under the Scotland Act 1998, Scotland has its own government that is responsible for most of the day-to-day issues there, including the justice system.
At a joint news conference earlier Tuesday, both Obama and Cameron blasted the decision by Scottish authorities to release al Megrahi.
Cameron promised that the British government will cooperate with a U.S. congressional investigation into the controversy, though he stressed that the decision to release al Megrahi was made by the Scottish government without any involvement from BP.
"There is absolutely no harm to be done in giving the fullest possible explanation" regarding the decision to release al Megrahi, Cameron said. He called the release a "misguided decision" by Scottish authorities.
Obama said most Americans were "surprised, disappointed and angry" about the decision to let al Megrahi go.
"We should have all the facts," he said, adding that the decision "ran contrary to how we should be treating terrorists."
The four senators said that questions over how al Megrahi could have survived almost a year and whether BP exerted influence in the case need to be answered. The Scottish government has insisted that BP never lobbied to free al Megrahi.
"We say there is a lot of circumstantial evidence -- no smoking gun -- strong circumstantial evidence, that something wrong happened here," Schumer said. "We don't think all the facts have come out."
Schumer was joined by fellow New York Sen. Kirsten Gillibrand and New Jersey Sens. Frank Lautenberg and Robert Menendez. All are Democrats.
The senators released a letter Monday calling for the United Kingdom to launch a full investigation into al Megrahi's release and whether BP was involved.
BP has said it expressed concern to the British government in late 2007 about the slow progress of a prisoner transfer agreement that Britain and Libya were negotiating, saying it could have had a "negative impact" on British commercial interests.
But the company has denied involvement in any talks with either the British or Scottish governments specifically about al Megrahi's release.
At the senators' urging, the U.S. Senate Foreign Relations Committee has set a hearing date of July 29 to investigate all the circumstances surrounding the release of al Megrahi, including whether BP played a role. Gillibrand and Menendez serve on the Foreign Relations Committee. Menendez will chair the hearing.