What do you do with a captured terrorist? Throw him in the brig. That’s what was done with Ahmed Abdulkadir Warsame, the Somali who in April was plucked from a fishing boat off the East African coast between Yemen and Somalia.

Once you’ve got him, though, the legal troubles begin. Because the U.S. Supreme Court rejected the Bush administration’s vague plan of indefinitely detaining “enemy combatants” in Guantanamo without any hearing, the U.S. government was left with three lawful choices for what to do with Warsame:

It could have determined at a simple military hearing that he was part of al-Qaeda, with which the U.S. is at war, and detained him as a prisoner of war. It could have charged him with war crimes before a military tribunal. Or it could have filed terrorism charges against him in a civilian court -- which is what the Justice Department did to Warsame last week.

In bringing criminal charges against Warsame in New York City, the Justice Department no doubt meant to avoid adding another prisoner to Guantanamo, which President Barack Obama would like to close. But even this decision poses serious problems for the Obama administration -- and for the rule of law.

For two months after his capture, Warsame was questioned by intelligence officials aboard the assault ship USS Boxer. Then he had a four-day respite, during which the International Red Cross was allowed to visit him -- a right guaranteed to POWs.

Once the Red Cross was gone, Warsame was, for the first time, read his Miranda rights. And at this point Federal Bureau of Investigation personnel took over the interrogation. Surprise, surprise: He waived his right to keep silent or speak to a lawyer.

Constitutional Rights

This novel procedure means a court will probably have to decide whether Warsame’s statements to law enforcement may be used against him in court, or whether the setting and context of his confession make it involuntary. The administration says it gave Warsame four days off after his interrogation by intelligence officials in order to differentiate the questioning in which he lacked constitutional rights from the one in which he was entitled to them.

But after a person has been interrogated Guantanamo-style for two months, how could he be expected to believe that he really had the right to remain silent or to a lawyer? Deception is a standard part of interrogation by military or intelligence officers. Warsame would have had every reason to doubt that he really was being allowed any rights -- or that the change in his interrogators was anything more than a trick.

Add to this the likelihood that law enforcement knew, at least roughly, what Warsame had already told the intelligence officials, and it’s clear that his statements should almost certainly not be admissible in court.

Then there is the question of why Warsame isn’t being held as a POW or charged with war crimes. We are at war with al-Qaeda, which Congress has said includes all those who perpetrated or supported the Sept. 11 attacks. We are not, however, at war with all terrorists everywhere -- including the Somali rebel group Al Shabab. Membership in Al Shabab is therefore not grounds for POW-style detention.

The administration acknowledges this. But it also says we are at war with senior Al Shabab leaders “who adhere to al-Qaeda’s ideology” and might attack civilians outside Somalia. Warsame allegedly met with Anwar al-Awlaki, the U.S.-born Yemeni cleric who is part of al-Qaeda in the Arabian Peninsula. Warsame also allegedly received arms training in Yemen.

Operative Or Not

Perhaps Warsame’s captors initially thought he was close enough to al-Qaeda to be a lawful wartime target. The Department of Justice now says Warsame was a conduit between Al Shabab and al-Qaeda in the Arabian Peninsula. The fact that the Obama administration didn’t choose to detain him as a POW, though, suggests that officials may also have concluded, after interrogation, that he wasn’t really an al-Qaeda operative. They also seem to lack enough evidence of a war crime to try him for that.

If Warsame was not an al-Qaeda member, the administration had only one lawful option: to try him for conspiracy to materially support terror. His alleged crimes, it seems, stem from his membership in Al Shabab -- a radical Islamist rebel gang that is waging an insurrection against Somalia’s transitional government -- and his training in Yemen, allegedly by al-Qaeda in the Arabian Peninsula.

Under international law, which applies in cases of war crimes, mere membership in a terrorist group isn’t a crime, and there is no crime of conspiracy. But U.S. law is different. If the U.S. wants to make it a crime for a Somali to conspire to support terrorism in Somalia, it can. If it can convince a New York jury that the government is right to designate Al Shabab as a terrorist group, it can convict Warsame of conspiracy to support terrorism merely for belonging to it.

Warsame may well be a dangerous terrorist. But it also seems possible that he just had the bad luck to be caught, then to be found not to be at war with us, rendering him ineligible for detention or a war crimes tribunal. As a POW he would in theory be eligible for future release. But by releasing him the U.S. would risk embarrassment were he to commit terrorist acts in the future.

So Warsame will go on trial under the considerably looser standards of conspiracy. There may be evidence against him other than his statements. But that evidence may not be admissible in court. His fate may well rest on whether his statements after he was issued the Miranda warning are admitted as evidence.

If they are, he will probably be convicted, and then he will spend the rest of his life in prison. That may be a victory for the rule of law -- but somehow it doesn’t quite feel like one.

(Noah Feldman, a Bloomberg View columnist, is a professor of constitutional and international law at Harvard and the author of five books, most recently “Scorpions: The Battles and Triumphs of FDR’s Great Supreme Court Justices.” The opinions expressed are his own.)

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To contact the author of this column: Noah Feldman in Cambridge, Massachusetts, at noah.feldman@harvard.edu.

To contact the editor responsible for this column: Mary Duenwald mduenwald@bloomberg.net.