The federal courts and military tribunals that will prosecute suspected terrorists vary sharply in their independence, public stature and use of evidence. But the Obama administration has so far offered no clear-cut rationale for how it chooses which system will try a detainee.
The fuzzy line drawn by the administration has made it easier for critics on both the left and right to assert that no firm legal principle is guiding the choices.
The administration has said similarly situated suspects can be tried in either system, while others may still be held without trial because there is insufficient evidence for either proceeding, but they are considered too dangerous to release.
"I think the Obama administration is trying to straddle this debate between whether we should approach al-Qaida as a problem of massive-scale criminality or as a problem of war," said Matthew Waxman, a former Bush administration State Department and Pentagon official now at Columbia University law school.
Indeed, on Capitol Hill last Wednesday, Attorney General Eric Holder testified, "The 9/11 attacks were both an act of war and a violation of our federal criminal law, and they could have been prosecuted in either federal courts or military commissions."
The administration is sending professed Sept. 11 mastermind Khalid Sheikh Mohammed and four alleged henchmen to a civilian trial in New York, while a suspect in the USS Cole bombing in 2000 and four other terror suspects will be tried by military commissions.
The major differences between the systems are the federal judiciary's independence, rooted in the Constitution and lifetime appointments of judges, and the relaxed rules for admitting evidence in military tribunals.
Federal courts bar evidence obtained by coercion. And the new law regarding military commissions that President Barack Obama signed last month forbids evidence derived from torture and other harsh interrogation techniques. But the commissions still have rules that allow greater use of hearsay testimony and, in some instances, could permit the introduction of coerced testimony.
Military judges ultimately will decide what evidence can be admitted, but the new law allows statements made by defendants to be used even if they are not given voluntarily in certain circumstances, including in combat situations. Written witness statements, rather than live testimony that is subject to cross-examination, also can be admitted by military judges.
The larger issue, for some civil libertarians, is what the American Civil Liberties Union's Jonathan Hafetz called a "legitimacy deficit."
The commissions set up under President George W. Bush to try terrorism detainees have been revised several times based on Supreme Court decisions and acts of Congress that moved their rules and procedures closer to federal courts.
"But they just don't have the credibility and never will have the credibility that federal courts have," Hafetz said.
Joanne Mariner, director of the terrorism and counterterrorism program at Human Rights Watch, said another indication of the reduced stature of the commissions is that, by law, they can never be used to try U.S. citizens.
"The federal courts are a co-equal branch of government and judges are constitutionally protected from interference. That is really important in politically charged and high-profile cases," Mariner said. "Military commission judges and prosecutors have no such protection."
On the other hand, supporters of the military tribunals say they provide sufficient protections for accused terrorists. Moreover, they say, the Sept. 11 attack is a classic war crime _ the mass murder of civilians _ for which military tribunals have traditionally been used.
"Other things being equal, you would think that targeting civilians makes the crime more grave," said Gregory G. Katsas, a Bush Justice Department official. "If you don't try Khalid Sheikh Mohammed by military commission, I don't know who you try."
A host of leading Republicans, including Bush's last attorney general, Michael Mukasey, and former New York Mayor Rudy Giuliani, have said the 9/11 defendants should be tried by military tribunal.
The administration appears to have made pragmatic and political choices after determining that it is likely to win convictions in a civilian trial of the alleged Sept. 11 plotters, but seems less sure of its prospects if suspects from other attacks were tried in federal court.
Holder hinted at this balancing act in his Senate Judiciary Committee testimony.
"I am a prosecutor, and as a prosecutor my top priority was simply to select the venue where the government will have the greatest opportunity to present the strongest case in the best forum," he said, while rejecting senators' assertions that convictions are easier in military commissions.
But he also said those who attacked a civilian target on U.S. soil were being sent to a civilian federal court and those who attacked or plotted against military targets abroad were going before tribunals.
Holder's formulation puts the U.S. in the position of distinguishing between American interests based on which government agency was attacked. The attack on a Navy warship, the Cole, is to be handled by military commission, while the bombings of U.S. embassies in Africa in 1998 have been prosecuted by successive administrations in federal court.
Waxman said that it is unlikely al-Qaida makes that distinction. "We're talking about a transnational terrorist network whose criminality extends across borders," he said. "The scene of the crime is global."
The lack of a clear explanation of the administration's choice has led some legal experts to conclude federal courts will be used when convictions seem assured and commissions will handle cases where evidence is weaker or more difficult to get past a federal judge.
"It somewhat supports the idea that if we can't make the case, we'll send them to a second-class system, which is the military commission," said Laura Olson, senior counsel at The Constitution Project, which objects to using military tribunals.
This two-tiered system may not entirely satisfy civil libertarians who want the administration to abandon the commissions or the Republican-led opposition in Congress that objects to giving Mohammed and the others their day in federal court.
But it could prove a viable approach that both avoids the credibility problems of using commissions for the highest visibility cases and the risk of acquittals if less devastating attacks were tried in civilian courts, said University of Chicago law professor Eric Posner.
"This moderate view that avoids the two extremes may be very appealing to people in the long run," Posner said.