New York (CNN) -- Two U.S. senators ratcheted up the pressure on BP and British government officials Monday to provide answers to the questions now swirling around the release of Abdelbaset Ali Mohmed al Megrahi, the Libyan man convicted in the 1988 bombing of Pam Am Flight 103, which killed 270 people.
Obama administration officials, meanwhile, took what was described as an "exceptional step" to make clear that they had strongly opposed al Megrahi's release.
A group of senators from New York and New Jersey 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.
Robert Menendez, D-New Jersey, is set to lead a Senate Foreign Relations Committee hearing Thursday on the controversy surrounding al Megrahi's release. Several British officials have declined invitations to testify.
"The abundance of incredible coincidences" surrounding al Megrahi's release demands transparency, Menendez said Monday. "A cloud of suspicion" will hang over the issue until all of the relevant questions have been answered.
Menendez accused the Scottish and British governments of trying to point the finger of blame at each other in the decision to release al Megrahi. They're "playing a game of diplomatic tennis worthy of Wimbledon," he said.
Sen. Kirsten Gillibrand, D-New York, said she is concerned that the release was "an example of profits being put above people."
The senators need to know if "blood was given for money," she said. "We need to know that justice was served in this case."
The two senators were joined by relatives of three of the victims of the bombing.
"The increasing silence" of authorities in London and Edinburgh leads me to "think one thing: They're guilty of something," said Eileen Walsh, who lost her father, brother and sister.
Menendez and Gillibrand were part of a group of four senators who met for 45 minutes last week with Prime Minister David Cameron, asking the British leader for an independent investigation into the release of al Megrahi and any possible involvement BP might have had. Sens. Charles Schumer of New York and Frank Lautenberg of New Jersey also attended.
Most of the bombing victims were Americans. The flight was headed from Frankfurt, West Germany, to New York via London, England, when it exploded in the air.
Al Megrahi was convicted in the case and sentenced to life in prison. The Scottish government released him on compassionate grounds in August after doctors said he had terminal prostate cancer and just three months to live. Al Megrahi is still alive, however, and news reports in recent days have questioned whether he was as sick as depicted.
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.
Menendez has invited Scottish Justice Secretary Kenny MacAskill, who made the decision to release al Megrahi, to testify before the Foreign Relations Committee.
Andrew Fraser, the physician who gave the prognosis that led to al Megrahi's release, and former British Justice Secretary Jack Straw also have been asked to attend. All have declined.
In an effort to make clear that the Obama White House had opposed the release al Megrahi, the State Department on Monday released the text of an August 12, 2009, letter sent from Richard LeBaron, the number two official at the U.S. Embassy in Britain, to Scottish First Minister Alex Salmond.
The letter stated that the U.S. government "maintains its view that in light of the scope of Megrahi's crime, its heinous nature, and its continued and devastating impact on the victims and their families, it would be most appropriate for Megrahi to remain imprisoned for the entirety of his sentence."
If al Megrahi were released from prison, the United States would strongly oppose allowing him "to travel outside of Scotland," LeBaron wrote. "We believe that the welcoming reception that Megrahi might receive if he is permitted to travel abroad would be extremely inappropriate."
State Department spokesman P.J. Crowley said Monday that the administration was trying to "avoid the worst possible outcome -- a hero's welcome for Megrahi in Libya. ... Unfortunately, the Scottish government did not heed those views. Scottish authorities instead took two steps we explicitly asked them to avoid: they released Megrahi and they permitted his return to Libya."
At a joint news conference last week, Cameron and U.S. President Barack Obama blasted the Scottish decision.
Cameron promised that the British government will cooperate with the 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.
Obama said that most Americans were "surprised, disappointed and angry" about the decision to let al Megrahi go.
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.