Admiral Mullen said he was "appalled" by the decision, which he said was clearly "political."
"Your action makes a mockery of the rule of law," Mr. Mueller wrote. "Your action gives comfort to terrorists around the world who now believe that regardless of the quality of the investigation, the conviction by jury after the defendant is given all due process, and sentence appropriate to the crime, the terrorist will be freed by one man's exercise of 'compassion.' "
The Telegraph calls the Lockerbie fallout a "test" of the famous "special relationship" between the US and the UK: "With President Obama and Secretary of State Hillary Clinton also lining up to criticize the decision, it is now easier to count the senior American figures who have not spoken out than those who have."
Scotland feels the heat
Scotland's first minister, Alex Salmond, who effectively functions as a prime minister, rejected Mueller's criticism and defended the release.
"Obviously there's a great deal of disappointment and hurt among many people in the United States about our decision to grant compassionate release to the Lockerbie bomber," Mr. Salmond told Sky News on Sunday. "We understand that, we recognize that ... but the process of compassionate release doesn't depend on the guilt or innocence of the party. It's an evaluation based essentially on the medical condition of the prisoner."
But former First Minister Jack McConnell called the decision a "grave error of judgement" that had damaged Scotland's reputation and "brought shame on the country."
And, in a move reminiscent of the "Freedom Fries" episode (remember that?), there's even a website called boycottscotland.com that urges Americans not to buy whiskey and to visit Ireland instead of the UK.
'Deal in the desert'?
Adding to the sense of outrage in the US – and in Britain – are allegations that the British government bowed to pressure from Libyan strongman Muammar Qaddafi in order to secure better trade deals with the oil-rich nation.
Mr. Qaddafi's son, Saif al-Islam Gaddafi, said in a Libyan television interview Friday that Megrahi's release was linked to negotiations over oil and gas contracts.
The comments come amid reports in the British press that the release may have been linked to the famous "deal in the desert" in 2007 between Qaddafi and former Prime Minister Tony Blair.
That deal, reports The Times of London, "was a significant step towards Libya’s rehabilitation among world leaders after it was held responsible for the [Lockerbie bombing], and also helped to clear the way for BP to invest £450 million [$742 million] in exploring Libya’s vast untapped reserves of oil."
Foreign Secretary David Miliband has dismissed the idea that the British government pushed Scottish authorities to release Megrahi in order to smooth Libya-UK ties as “a slur."