By Ken KlukowskiFellow and Senior Legal Analyst, American Civil Rights Union

The first terrorist detained in Guantanamo Bay is on U.S. soil and is now in the civilian court system. Democratic officials and operatives are lauding President Obama's commitment to close Gitmo. They say that we can simply lock up all these convicted terrorists in U.S. federal prisons. But one question exposes the fatal flaw with this plan: What convicted terrorists?

The Fifth Amendment of the U.S. Constitution forbids any person being "deprived of life, liberty, or property, without due process of law." For over 200 years, this has meant one thing: Aside from pre-trial confinement, no one can be thrown in prison without first being convicted in a court of law.

Ahmed Ghailani, the terrorist who had his preliminary hearing in New York today, is only now beginning his court process. Like him, all of the terrorists in Gitmo have not been tried in court. Therefore they have not been convicted of anything.

That's why President Bush was advised that these terrorists had to be sent to Gitmo. Because the terrorists were being held by the U.S. military (instead of police), on a military base (instead of a prison), on Cuban soil (instead of U.S. soil), these terrorists could be held until they were no longer a threat.

President Bush was advised that these terrorists could be held indefinitely by the U.S. Marines at Gitmo as unlawful combatants. The writ of habeas corpus gives those covered by the writ the power to demand that they either be charged with crimes and given a judicial proceeding to beat those charges, or be immediately released. Habeas has always extended to U.S. citizens and to people held on U.S. soil, but never to foreigners held on foreign soil. Hence, Gitmo.

This was all undisputed before the 2008 Supreme Court decision Boumediene v. Bush, which extended the writ of habeas corpus to these terrorists. The Boumediene opinion allows these terrorists to demand judicial review of their confinement, and thus that the U.S. government must free them if it cannot prove its case.

But what President Obama does by bringing these terrorists to U.S. soil is provide all sorts of additional rights to them. Habeas does not automatically confer all criminal procedural rights in the Constitution. But a person being held in a federal prison on U.S. soil has a much stronger claim to every single one of those rights.

These rights include that the person is presumed innocent, and the right to a taxpayer-funded lawyer. It also includes that the government must prove every element of a crime beyond a reasonable doubt, that a conviction requires a jury verdict, the right to compel any witnesses against him (such witnesses would be U.S. soldiers) to appear in the courtroom and take the stand under oath. The terrorist's lawyer can challenge and discredit the soldiers. Confessions the terrorist made before being given a lawyer are inadmissible. Hearsay is inadmissible. Mishandled evidence is inadmissible. If other people were in the "crime scene" (that is, the battlefield, where there were probably lots of people), then it could be contaminated, rendering that evidence inadmissible.

If the government cannot prove any aspect of its allegations, the terrorist goes free. And if the government is does not provide a speedy trial, the terrorist goes free.

The American justice system is designed to heavily favor defendants. Our criminal justice system is structured on a simple principle: It is better for a hundred guilty criminals to go free than for a single innocent person to be condemned.

In short, it's a legal nightmare for going after foreign terrorists. That's why we don't give foreign terrorists a civilian trial. This is war, not law enforcement. The civilian system is no way to win a war.

Think this sounds far-fetched? Then ask yourself one question: Why are there now FBI agents in Afghanistan giving Miranda warnings to terrorist detainees, advising them that they have the right to remain silent and the right to an attorney (funded by taxpayers, of course)? That's not something soldiers do in a war, but it is something that law enforcement officers do with criminal defendants.

Although President Obama says he will use military commissions for some terrorists, bringing them on U.S. soil could give them the right to object to such tribunals. And forget about detaining any of them without a trial.

To be sure, some terrorists will be convicted under our civilian system. We surely have plenty of irrefutable evidence against many of them. No doubt the administration will start with a few terrorists against whom we have mountains of evidence. But dozens, and possibly hundreds, will go free. And if other countries won't take them (and who wants to take hardened terrorists?), then they will be set free on the streets of America.

So yes, we would eventually have some convicted terrorists, and they could go to a federal prison somewhere. But none have been convicted thus far, and many will end up going free, maybe coming to a town near you.

Ken Klukowski is a fellow and senior legal analyst with the American Civil Rights Union.