London, England (CNN) -- Two U.S. senators from New Jersey intensified their calls for the British and Scottish governments -- and oil giant BP -- to provide information surrounding the circumstances of the convicted Lockerbie bomber's release a year ago.
The British government urged Libya on Friday not to celebrate the anniversary of the convicted bomber's release, saying it would be "offensive and deeply insensitive" to the families of the 270 people killed in the 1988 bombing of a Pan Am flight over Scotland.
Also Friday, the Obama administration again blasted the decision by Scotland to release Abdelbeset Ali Mohmed al Megrahi from prison exactly a year ago on compassionate grounds due to a diagnosis of terminal cancer.
"As we have expressed repeatedly to Scottish authorities, we maintain that al Megrahi should serve out the entirety of his sentence in prison in Scotland," Secretary of State Hillary Clinton said in a written statement.
President Barack Obama's assistant on homeland security and counterterrorism, John Brennan, called the release of al Megrahi "unfortunate and inappropriate."
Democratic Sens. Robert Menendez and Frank Lautenberg noted al Megrahi was only given three months to live when he released, but he is still alive today.
Menendez noted that on August 20, 2009, al Megrahi stepped off a plane into the arms of a cheering throng in Libya.
"A mass murderer tasted freedom, experiencing joy," Menendez said. "It was a scene that made the stomach turn ... that made old wounds fresh again in the hearts of those whose family members died at the hands of that man."
Lautenberg said, "It is the families of those victims who deserve compassion, not this terrorist."
"Al Megrahi ... is very much free, living in the lap of luxury by all accounts," Menendez said. Doctors who examined the convicted terrorist in prison now say he could live another 10 years, he said.
The case has outraged many on both sides of the Atlantic, and led U.S. senators to demand answers from Scotland about the details of his release.
Menendez said his office has sent letters to British Prime Minister David Cameron and Scottish First Minister Alex Salmond, "laying out those areas where questions linger" and asking for additional answers and documentation.
Scottish authorities have defended their actions in the case, saying Justice Secretary Kenny MacAskill relied on a medical report from the top doctor in the Scottish Prison Service, along with reports from the parole board and prison governor, in deciding to free al Megrahi, who had been serving a life sentence.
"We took the decision in good faith," Salmond told Sky News on Friday. "We followed the judicial processes, the law of Scotland and the jurisdiction the Lockerbie atrocity has been governed [by], not for the last year, but for the last 20 years."
Under the Scotland Act of 1998, Scotland has its own government that is responsible for most of the day-to-day issues there, including the justice system. It took charge of the case because the flight al Megrahi was convicted of bombing exploded over the Scottish town of Lockerbie.
Scottish authorities have insisted that three doctors hired by Libya to assess al Megrahi's condition last year played no part in the decision to release him. Menendez said he wants to know what was discussed when the doctors met with Libyan officials.
Dr. Andrew Fraser, the director of health and care at the Scottish Prison Service, also said the three-month prognosis was a reasonable estimate.
U.S. senators also have repeatedly voiced suspicions that Scotland released al Megrahi as part of a deal allowing BP to drill off the Libyan coast. Salmond has already shot down such concerns, saying "there is no evidence whatsoever" of any link.
Menendez plans to chair a U.S. Senate hearing in September on the controversy surrounding al Megrahi's release.
Friday, Menendez said the senators have asked the British and Scottish governments to conduct an independent investigation in the United Kingdom, which he said Cameron supported before he became prime minister.
Lautenberg called on British and Scottish officials to stop "stonewalling and side-tracking."
"Help us clear the air; help us give information to the families."
Menendez also said letters are being sent to Libyan and Qatari leaders, inquiring whether "commercial interests" led them to pressure Britain and Scotland to release al Megrahi.
Al Megrahi is the only person ever convicted in the bombing of Pan Am Flight 103, which exploded over Lockerbie in December 1988, killing 259 people on the plane and 11 on the ground.
Most of the dead were Americans. The flight had been heading to New York from Frankfurt, Germany, via London, England, when it blew up.
A special Scottish court in the Netherlands convicted al Megrahi in 2001.