It used to be innocent until proven guilty. But the war on terror is changing how the US polices its own citizens, with ritual humiliations at airports and suspects being locked away without charge. Patricia Williams argues that we must not let our leaders use fear of the unknown to curtail fundamental civil liberties

The information card the American Civil Liberties Union hands out to citizens titled "What To Do If You're Stopped By The Police" states: "Ask if you are under arrest. If you are, you have a right to know why." And then there are the tenets we Americans have all grown up knowing: our basic constitutional rights.

Unfortunately, that little litany is facing serious ridicule in some quarters of late, scoffed at as antiquated in comparison to shiny new notions that promise fast-track delivery of expedited justice. And so the assumption of innocence until proven guilty is under attack as inefficient in an era of terrorism. The right to a lawyer, so essential in holding the state to its burden of proof, is under attack as an indulgent frill subsidised by the terminally naive. Even the very option of a trial is being questioned as many Americans have begun to reconfigure all criminality as a species of active warfare.

To a large extent, this new cynicism is driven by deep fear. It is understandable given our newly heightened sense of an embattled world. But that's what our constitution has always been there for: to act as a buffer in times when we are driven by fear, too tempted by the easy promise of rough-and-ready justice. Moreover, those constitutional safeguards embody the best traditions of Anglo-American jurisprudence. Habeus corpus , due process, the body of civil rights and, by extension, human rights - these represent the core of our shared values, the bedrock of our democratic ideals. It is my great concern that some part of that shared tradition is endangered as never before by the panic of these times. I am aware that this is a wild and dangerous world. But I am also afraid that we will lose what is most precious in our democracy if we allow the balance between freedom and security to tip too far toward the latter.

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The Bush administration has repeatedly defended its power to detain enemy combatants not simply in the war against Al-Qaida or Afghanistan or Iraq or North Korea but "in this war on terrorism". That phrasing means that war is suddenly a much broader concept than we have known before. In January, a US judge ruled that Yassir Hamdi, a US citizen captured in Afghanistan, could be held indefinitely, without charge and without access to a lawyer. Jose Padilla, another US citizen, was captured, not on a battlefield but in O'Hare airport in Chicago. He has been in a military brig for nine months now without any formal charge (although attorney general John Ashcroft's justice department has publicised its conviction that he was planning to detonate a so-called dirty bomb).

This strategy of detention is the logical if monstrous offspring of suspect profiling, which, when unsustained by evidence, is nothing less than the substitution of a presumption of guilt for the presumption of innocence.

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Without the legal counsel historically guaranteed, even in military tribunals, we as citizens are licensing a shadow intelligence force that can hold people until they literally rot in jail - or can somehow prove themselves innocent without the "coaching" of lawyers. In President Bush's January 28 State of the Union speech, he directly addressed this newly expedited status of the presumptively guilty suspect: "All told, more than 3,000 suspected terrorists have been arrested in many countries. Many others have met a different fate. Let's just put it this way: they are no longer a problem to the United States and our friends and allies."

I am nagged by the question posed by a letter in The New York Times that focused on Bush's seeming "implication that the murder of suspects in such circumstances is not only allowable but a thing to be proud of. What would happen," asked the letter, "to the police chief of a large city if he declared that 'suspected terrorists' were being dispatched in such a manner?"

What indeed happens if police act as though they're at war, or when the executive branch of the most powerful nation on earth begins to employ the tactics of what we had, until very recently, agreed were corrupt backroom tactics of overly stressed urban policing. Perhaps it is not an apt analogy - I am not an expert in international affairs - but let me offer a cautionary example that I think may be an instructive object lesson.

It was a street crimes unit under intense, at times hysterical, public pressure to make New York safe for tourism that led to the arrest and conviction of five men in the so-called Central Park Jogger case. In 1991, a stockbroker was jogging in Central Park at about 9 o'clock at night. She was brutally beaten and raped and very nearly died. The jogger remembered nothing. The police arrested five African-American teenagers who had been in the park at some point within 12 hours of the assault. Confessions were obtained from four of them, although there was no other evidence to place them at what was an extremely bloody and muddy crime scene. All the young men were convicted. Their obligingly sullen faces were melded with the newly coined notion of "wilding" - that is, of rampaging "young black males" who were taking over the city. That notion in turn justified a degree of racial "profiling" on an unprecedented scale.

Only in the past few months has it come to public light that DNA evidence implicates a serial rapist who has confessed to committing the crime alone.

The police department hastily countered with a report insisting that the original defendants must have been involved in something. But the police department's belief, however sincere, is no substitute for hard evidence.

That is why we keep things public, put things to the test in a court of law, however imperfect.

First, the defendants did not have adequate representation. The defence attorneys were almost comically incompetent. Second, the defendants never should have been tried together. They were too easily depicted as a clotted unit - the "wild-ers", a singular pack, five individuals melded into one hyper-horrific presumptively suspect profile. If we think such imagery will not be a factor in military tribunals where access to counsel of one's choice is not provided we are naive indeed.

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Third, the confessions were questionable, and no one seemed to care. They were preceded by 18 to 30 hours of non-stop questioning, sometimes under quite unorthodox circumstances. For example, one 14-year-old was put in the back of a police car and driven around the park in the middle of the night.

The confessions themselves were filled with inconsistencies and obvious factual errors that no one took seriously until now. Most troubling, the first handwritten drafts of the confessions were in police-speak. It seems that one detective wrote down three of the four incriminating confessions before they were videotaped. My notes of that detective's testimony reveal that he didn't "know if I substituted Ramon's words for my own, but I wrote down what I recall". The male black? "Probably my words." Female white? "He probably said white female. Or white girl." Had sex? "I don't recall if those were his words or mine." If we think such practices will not be a far greater problem in interrogations of enemy combatants with no review at all, we are doubly naive.

Fourth, there was no physical evidence. Indeed, aside from the confessions, there was no evidence of any sort. This was an extraordinarily bloody crime - the jogger lost about three-quarters of the blood in her body - and the scene was a particularly muddy one. But there was no blood on any of the accused, nor were any of their footprints found at the scene. Although the district attorney, in her final argument, argued that hairs from the jogger were found on two of the defendants, the actual testimony of the forensic analyst was never so conclusive. Rather, he said the hairs were more consistent with Caucasian hair than African-American. But this point sailed over the heads of the many in the courtroom.

When I hear that a lot of New Yorkers still believe that these five men were somehow involved in some criminal activity somewhere in the park that night, I hear the same sort of rationalising that has fed such apathy to the more thoughtless of our anti-terrorism policies. In this, as in all cases, if there is evidence of criminality, we should prosecute. But if there is no evidence, our suspicions, fears and insinuations are no substitute. I appreciate the need to balance security against freedom, but in such cases I worry that unlimited, secret and unreviewed detentions are short-sighted, self-serving and, in the long term, as dangerous to democracy as terrorism itself. And I do not say that lightly.

In the Central Park Jogger case, the prosecutors were scared. The police were scared. The public felt "terrorised" by crime in New York City. But in addressing it, something awful happened. Police started picking up anyone who frightened them. A majority of the public called for tough laws with fewer protections for defendants. Racial profiling told us who to be afraid of before they did anything. There was a vast public acceptance of bad police practices rendered by stressed, frightened, badly trained officers.

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The result is a deep racial, cultural and class divide, particularly between black and white. Both sides want protection, but only one gets it.

Then September 11. Suddenly the fear spread past Harlem, past South Central, past the South Side. Round 'em up goes global.

It's a scary little world right now. Such great edginess eats away at our capacity to reason. A friend who's an educator says that one of the questions they ask children in IQ tests is what they would do with a wallet if they found it on the street. The high-scoring answer is to find a police officer and hand it over. But black children, especially boys, almost never say that. They'd take it to their mothers or another female relative to have them turn it over. They tend to avoid police officers and try not to have their names in any public agency's files, especially the police's. But taking the wallet to your mother in the race-blind context of standardised tests is a sign of immaturity. Little boys run to their mothers. Big smart fearless boys take things directly to the men in charge. Thus "common" sense exists in complicated relation to value systems of coded fear, encrypted credibility. I worry that we are all at risk of becoming more childlike, more intimidated, less able to deal straightforwardly with the big men in charge.

I feel this new tentativeness every time I fly. I flew to Philadelphia recently and went through all the abasements of airport security, a ritual cleansing of the sort that until recently was practised only at the gates of maximum security prisons: I removed my shoes. Take off your coat, they instructed. We know there is good reason for it. We are polite. A guard in a rakish blue beret bestowed apologies like a rain of blessings as she wanded my armpits. "You have an underwire in your bra?" she asked. "You mind if I feel?" It is hard to be responsive to such a prayer with any degree of grace. It is ceremonial, I know. ButI I do mind. Yet I know I'll end up in strip-search hell if I go down that route. I was polite. I obeyed. "Not at all," I intoned, as though singing in Latin.

Over at another table, a different agent was going through my bags. He removed my nail clippers from the intimacy of my makeup pouch and discarded them in a large vat. The agent put on rubber gloves and opened my stainless steel Thermos and swirled the coffee around, peering into it with narrowed eyes. When he picked up my leather-bound diary and flipped slowly through the pages, a balloon of irreligiosity exploded at the back of my head, and I could feel my hair rise up. "My diary?" I said as evenly as I could.

"This is getting to be like the old Soviet Union." "So, you visited the Soviet Union?" he asked, a glinty new interest hardening what had been his previous languor.

I finally got to where I was going. On my way back, I wasn't searched at all. They stopped the woman just in front of me, though, and there she stood, shoeless and coatless, with the tampons from her purse emptied upon the altar of a plastic tray. Once on the plane, she and I commiserated, and then the oddest thing happened. Others around us joined in about how invaded and humiliated they felt, all angry at the overseers, all suspicious, all disgruntled and afraid.

I was, I admit, strangely relieved to see that we were not all black or brown; we were men and women, white and Asian, young kids, old designer suits. There was a weird, sad unity in our vulnerability, our helplessness.

But there was a scary emotional edge to the complaining, a kind of heresy that flickered through it, too.

If I'm right that we're in for a long stretch of backlash and retrenchment, what will matter most is the ability to endure the long-term powerlessness.

What will matter now is how to be resilient, persistent, even when reform is not likely to come about for decades. Now is certainly a moment to build broader and more complex coalitions than we have seen in recent years, for the political forces with which we must grapple are broader and more complex. The technology of population control alone ensures that this will be so.

For example, with a proposed computer system called Total Information Awareness, the Defense Advanced Research Projects Agency has plans to profile loads more Americans than just young black men. The system has the capacity to scan, without search warrant, our emails, credit card and banking statements, medical records and travel records. It is said that they'll be searching for "patterns" that suggest terrorist activity, a description that does not adequately convey the fear we ought to feel now that citizens are about to be surveilled not for law enforcement purposes but for military ends. Bear in mind that those computerised search engines are very much like spellcheckers in their search for "pattern". This morning, I happened to type the name "Amanda" in an email I was sending.

The spellchecker wanted to know if I didn't mean "armadillo". I worry that the military's spellchecker will want to know if I didn't really mean "armada".

But we must not make the mistake of spending more time watching our words than those of our elected representatives, our leaders, our guardians. I am not so cynical as to doubt that our leaders are doing what they can in the midst of this ungodly global mess. Nor, on the other hand, am I so naive as to assume my few words are much more than a vain murmur in the face of events so overwhelming. But, again, I speak not in vanity, but because I feel I must, as a deep believer in the obligations of citizenship, and as one who is committed to the fundamental values of democracy.

Let me end with playwright Arthur Miller's warning that we not turn our civic engagement into a crucible where "(a) political policy is equated with moral right, and opposition to it with diabolical malevolence". Once such an equation is effectively made, society becomes a congeries of plots and counterplots, and the main role of government changes from that of the arbiter to that of the scourge of God.

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Patricia J. Williams is professor of law at Columbia University in New York City. This article is an abridged version of her lecture at this year's Oxford Amnesty Lectures, supported by The THES .