When alleged "dirty bomb" plotter Jose Padilla arrived in the US, federal agents took him into custody with all the precision of a Swiss watch.
It was not a last-minute operation. Mr. Padilla, a US citizen, had been a prime target of investigators for weeks as he crisscrossed Europe and the Middle East.
But rather than obtaining an arrest warrant by demonstrating to a judge that federal authorities had probable cause to believe Padilla was planning mass murder, they instead relied on an obscure federal law designed to guarantee the presence of a key witness at a criminal proceeding.
By labeling Padilla a "material witness" in an ongoing grand jury investigation of terrorism, US officials were able to whisk him off the streets and into a high-security prison cell with minimal law-enforcement effort.
Since the terror attacks on Sept. 11, the so-called material-witness statute has emerged as a key and highly controversial weapon in the legal arsenal being used to wage the Bush administration's war against terrorism in America's homeland.
Supporters of this approach say it is justified by the continuing threat of massive civilian casualties posed by Al Qaeda and its operatives.
Critics see it as a direct assault on fundamental American freedoms. In the Padilla case and others, federal agents and prosecutors were able with the stroke of a pen to bypass many of the constitutional and statutory safeguards carefully enacted by Congress to protect citizens from the dangers of an overzealous national police force.
Just as a presidential designation of someone as an "enemy combatant" can trigger indefinite military detention without any formal charge, federal prosecutors are accomplishing that same result of indefinite detention without charge by relying on the material-witness statute, legal experts say.
Ronald Carlson, a law professor at the University of Georgia and a leading authority on material-witness law, says the Bush administration has adopted a flawed approach to the federal statute. "Material- witness laws came into being for one purpose and one purpose only to ensure that a witness who saw or knew something would be around for testimony at a criminal proceeding against a defendant," Mr. Carlson says.
"The problem is the Bush administration views these laws as part of a continuum in how you investigate defendants," he says. He adds that there is potential for abuse. "Sometimes these laws are used by the authorities to coerce information."
The advantages in fighting terrorism are obvious, experts say. Rather than having to prove probable cause of criminal involvement, all the government must show to authorize the open-ended detention of any individual is that prosecutors believe the "witness" possesses critical information related to the government's investigation and that he or she is unlikely to comply with a subpoena to testify.
Some legal experts say the witness law offers the government an effective means of disrupting ongoing terror plots without having to exert the time and effort to develop solid evidence of illegal conduct. There is no risk of disclosing intelligence sources and methods. And some experts say the witness law can be used to pressure detainees into providing timely intelligence, regardless of whether the resulting information results in a solid criminal case later.
"We are using criminal laws like the material-witness statute in a whole new context of terrorism prevention," says Paul Rosenzweig, a former federal prosecutor and legal research fellow at the Heritage Foundation in Washington. "Our criminal laws are not designed to fight a war on terrorism," he says. "The government is using the tools that are presently on its books and available, and the fit isn't perfect."
But Mr. Rosenzweig says the administration's approach is appropriate given the exigencies of the war on terror. "I'm not one to cheer about everything the government does, but those who think things haven't changed since Sept. 11 are putting their head in the sand."
Because material-witness laws have rarely been the subject of major court challenges, there is no extensive body of case law delineating abuses of the federal statute, experts say.
For example, it remains unclear to what extent material-witness detainees have a right to see documents related to their detention, have a right to Miranda warnings, or even have a right to consult with counsel.
"The whole concept of holding people as material witnesses has a lot of potential for abuse," says Richard Samp of the Washington Legal Foundation, a conservative legal-advocacy group.
"But there has to be in this national-security area a certain play in the joint," he says. "When you have people who are intent on destroying our society, there aren't many people who think the government should have no basis for holding such people until [investigators] have gotten enough evidence to arrest them for a crime. That would be suicidal."
While the law's utility may be apparent in cases involving government attempts to disrupt a terror plot, the experiences of some detainees illustrate the downside of the administration's approach.
In one case, a third-year medical student from Saudi Arabia working at a hospital in San Antonio was held for 12 days in solitary confinement in a New York prison cell because his last name was similar to that of two of the Sept. 11 hijackers. The student's name is al-Hazmi. The hijackers were al-Hamzi.
In another case, an Egyptian student was held in prison for 30 days because federal agents suspected he had an aviation radio capable of talking to an airline cockpit in his hotel room near the World Trade Center on Sept. 11.
Rather than digging for probable cause before making an arrest, prosecutors simply had the student, Abdallah Higazy, taken into custody as a material witness. He was held in a prison cell, denied telephone access to family and friends, and offered multiple opportunities to confess.
Mr. Higazy repeatedly denied any knowledge of the radio. Prosecutors responded by charging him with making false statements to federal officials. At one point during an intense interrogation and polygraph exam, Higazy admitted the radio was his own and offered three different versions of how he had obtained it, according to a federal prosecutor's statements to a judge in the case.
But the "case" against Higazy fell apart when the real owner of the radio came forward. Further investigation by the FBI revealed that a hotel security official had lied when he told the FBI he found the radio locked in Higazy's room safe. The security official made up the story, according to his lawyer, in a misguided effort to help authorities make a case against someone the security official thought might be an Al Qaeda operative.
Justice Department officials refuse to disclose how many individuals have been detained as material witnesses in its terrorism investigation.
Some, like Padilla, who also uses the name Abdullah al-Muhajir, have refused to cooperate. Others have talked extensively, only to wind up charged with crimes as a result of their voluntary cooperation.
That's what happened to Osama Awadallah, a Jordanian student in San Diego. Mr. Awadallah was imprisoned for 83 days. He was eventually charged with making false statements to a grand jury because of his faulty recollection about the name of one of the Sept. 11 hijackers, whom he had met 18 months earlier and last seen a year before the hijacking.
Two months ago, a federal judge in New York threw out Awadallah's indictment and declared that the government had violated the letter and spirit of the material-witness law. "This broad reading of the material witness statute has led to serious abuses," wrote US District Judge Shira Scheindlin in her 60-page decision.
Attorney General John Ashcroft defends his department's broad application of the witness law and pledges to appeal the ruling to the Second US Circuit Court of Appeals in New York.
Depending on how the Second Circuit rules, a showdown at the US Supreme Court may be on the horizon.