He was relieved of duty on Saturday for a "loss of confidence in his ability to command."
Mansoor Adayfi lives under near-constant surveillance in Serbia and his legal status in the country is uncertain.
The government is relying on a shaky legal basis for bombing the Islamic State.
That leaves some of the current detainees stuck in a legal "no man's land," a federal judge said.
Trump's Supreme Court nominee spent years defending the government's right to imprison some people without charge.
“This is a repugnant attempt to rewrite history and normalize governmental abuse of power," a Japanese-American history organization said.
The president had said he would keep Gitmo open and "load it up with some bad dudes."
"Trump has explicitly endorsed indefinite detention rather than a detention 'informed by the laws of war,'" lawyers argued in a new legal filing.
An exhibit of art made by inmates on the island detention center has drawn harsh criticism from the Pentagon.
The ACLU will argue that by keeping the suspect’s name a secret, the government is effectively denying him access to justice.
Federal prosecutors argued Ahmed Abu Khatallah "hates America," is "guilty as sin" and is a "stone-cold terrorist."
No one has been sent to Guantanamo Bay in nine years. There are good reasons for that.
The White House and senior Republicans are calling for the New York terror suspect to be designated as an “enemy combatant”. Here’s what the term actually means.