A US government aircraft was waiting at Misrata airport when Al-Marimi arrived with a “loosely fitted cloth hood” over his head.
His escorts asked the FBI to hurry up because onlookers were watching and he was placed on board the plane.
The Libyan authorities handed over a plastic “trash bag” containing some of his belongings, including a Quran, a prayer rug, clothing, toiletries, and medicine.
On the flight to the US, the FBI questioned Al-Marimi, performed a “head to toe medical examination” and provided him with clean clothes and blankets, his lawyers said.
They claim the prime minister of the Tripoli-based Libyan government, Abdulhamid Dbeibah, later secured financial investment from the United States, including $16m (£12m) to secure Libya’s transition to a democratic state and a contract with US oil giant Honeywell International.
Al-Marimi argues that the process amounted to an unlawful rendition and forcible abduction, removing the Washington court’s jurisdiction over the case.
The defence says the militia group staged an illegal kidnapping when diplomatic negotiations stalled, in a process which showed “an utter disregard for Libyan law and sovereignty.”
His lawyers said: “This is not the rule of law.
“This is the rule of the strong. Mr Al-Marimi’s rendition sends a chilling message to the people of the world: ‘If we want you, we will take you’.”
They added: “Mr Al-Marimi must be returned to Libya.”