Nearly seven weeks ago, on Sept. 12, the man apparently surrendered to a rebel group in Syria, which handed him over to U.S. forces, according to officials familiar with his case. Since then, his name, age and other personal details, including a second country of citizenship, have been withheld, even from U.S. lawyers seeking to represent him. He is being held in a Defense Department "short-term facility" in Iraq, according to the Pentagon.
The case could also provide lawyers with a way to challenge the authority of the government to detain fighters captured in Syria using that same 2001 war legislation, because the Islamic State did not exist at the time.
Earlier this month, at the request of the American Civil Liberties Union, which wants to represent the captured fighter, U.S. District Judge Tanya S. Chutkan in Washington gave the department until Monday to tell her in writing why the organization should not be given access to him to advise him of his rights and provide him with legal representation.
"It's extraordinary for them to hold a U.S. citizen without access to counsel or a court and without charges," said Jonathan Hafetz, the ACLU attorney who filed the motion. "It's truly unprecedented and a clear breach of the Constitution."
A Defense Department spokesman, Air Force Maj. Ben Sakrisson, said last week that the government continues to withhold the detainee's identity and circumstances because "it's still an ongoing operation." Asked to elaborate, he said, "There are still a number of U.S. agencies looking at the circumstances of how he came to be detained" and what should happen to him now.
A Justice Department spokesman declined to comment.
The man was questioned first by an interagency interrogation team for intelligence purposes and then by an FBI team seeking enough admissible evidence to bring a case against him, according to officials who spoke on the condition of anonymity because of the secrecy surrounding the case. He refused to talk to the interrogation team and demanded a lawyer, the officials said.
He was then read his Miranda rights, and he again refused to cooperate and repeated his demand for a lawyer, according to people familiar with the case. And an additional complication emerged — Web postings suggested he may have done some reporting in Syria as opposed to being a fighter, these people said. But U.S. officials are skeptical of the idea that he is a journalist, they said.
While much about the man remains unknown, the officials said that he once had ties to the Pacific Northwest but that most of his family and roots are in the Middle East.
Without a confession, there is simply not enough evidence to charge the man in U.S. federal court, making it highly unlikely that he will be brought back here to face criminal charges, these people said.
Removing the likelihood of a trial in the United States leaves the government with few options, said William Banks, a professor of public administration and international affairs at Syracuse University. "It's time now to wonder whether the Trump administration is thinking of doing something different," he said.
Banks and other national security analysts said the United States could negotiate with the man's family and country of second citizenship to accept his return under conditions that he be monitored and not be allowed to travel.
Such deals have been struck in the past when, for instance, prisoners at Guantanamo Bay have been transferred home.
Other options, all carrying legal risks, include turning him over to Iraqi authorities.
But if there is too little evidence for a U.S. case, there is probably too little evidence to persuade an Iraqi court to convict him. Secondly, it is against U.S. law to send a prisoner to a country where he could be tortured.
"Torture is rampant in Iraq," said Belkis Wille, the senior researcher for Iraq at Human Rights Watch, who has visited some facilities for Islamic State prisoners and collected evidence of their treatment. "My strong assessment would be, he would get the death penalty and would be executed with a flawed trial and a defense attorney who makes no defense."
The Trump administration could consider sending him to Guantanamo Bay, but that, too, would invite immediate litigation.
"It would open the door to legal challenges the government just doesn't want to face," said Stephen Vladeck, a professor of national security law at the University of Texas. "The DOJ and DOD would be very nervous because of the precedent [a legal ruling against the government in a court challenge] could imply for the 41 other detainees" held there, allowing them all to challenge their detentions.
"The government is stuck. They are doing everything to stretch the clock to try to figure out the least worst position."
Rachel Weiner contributed to this report.