Bernhard Docke, the released man's lawyer, said: "The Americans are incorrigible, they have not learned a thing. He was returned home in chains, humiliated and dishonoured to the very end by the Americans,
"It was a giant American transport aircraft and he was alone in it with 15 US soldiers. He was chained down, his feet were chained, and his eyes covered."
Murat Kurnaz was not able to attend a news conference in his home town of Bremem on Friday because he was still suffering from the effects of his detention at Gunatanamo on Cuba.
Kurnaz was still living "in a sort of netherworld" after his ordeal. "Give him time. Yesterday was an extremely difficult day for him," Docke said.
"He was tortured. We just found out yesterday that for nine months he was kept permanently under a bright light round the clock. This light was never switched off," he said at a news conference broadcast live on national television.
Kurnaz said he suffered abuse at Guantanamo, and interrogation techniques including sexual humiliation, water torture and desecration of Islam.
Frank-Walter Steinmeier, the German foreign minister, said that an agreement on the release of Kurnaz had come after long negotiations between the US and German governments.
The US has been criticised by human rights groups and some of its allies for holding about 450 foreign terrorist suspects at the naval base in Cuba, many for four years or more and without charge.