Abu Zubaydah spent time at a “black site” in Poland. At some point during his multi-decade detention, he was tortured. All this is public knowledge. What the United States government has not done is officially acknowledged a link between the two.During the Supreme Court’s oral arguments in the case on Wednesday, the nine justices pressed Brian Fletcher, the US government’s lawyer, on why this “public knowledge” should still be treated like a secret. The answer, he said, was that the US had given its word to Poland to keep the information confidential.If it had been a domestic US case the calculus might be different, he said, but this involved a diplomatic agreement – and it was in US national security interests to honour its promises.Justice Elena Kagan was sceptical, calling it “a little bit farcical” to use a state secrets privilege to protect something that is no longer one.Several justices expressed frustration that the US government has been limiting Mr Zubaydah’s ability to testify on his own behalf. His account would be a much more direct way of establishing the link between Poland and torture. It was asked why, almost two decades after his capture and following the end of US military involvement in Afghanistan, was he still being held by the US at all?But that, Mr Fletcher said, was a matter for another court hearing on another day.