The U.S. is fighting a "war on terror," while Europe's battles against terrorists largely take place in the courtroom. Here is a look at the tensions in the trans-Atlantic relationship that have developed out of this pursuit of differing strategies.

Moroccan Mounir el Motassadeq is the only person ever to be convicted of taking part in the Sept. 11 attacks. Yet today he freely walks the streets of Hamburg, Germany.

Motassadeq was arrested in Hamburg in November 2001 and charged with 3,066 counts of accessory to murder for having wired money to the hijackers in the United States. In February 2003, he was found guilty and sentenced to 15 years in German prison.

But Motassadeq's conviction was overturned by a German appeals court in March 2004 because the United States offered evidence to the prosecution but not to the defense. The United States had provided the prosecutors with information based on interrogations of Ramzi bin al-Shibh and Khalid Sheikh Mohammed, two high-level detainees who allegedly devised the plot. But the U.S. refused to provide either the prosecution or the defense with the detainees themselves, their interrogators or full transcripts of what they said.

Motassadeq's former lawyer in the case, Gerhard Strate, said if bin al-Shibh and Mohammed were unavailable for security reasons, the prosecutors could instead provide transcripts of the interrogations or the ability to cross-examine the interrogators. The U.S. Department of Justice refused. It sent an FBI agent who answered questions about the nature of the attack, but not about the interrogations that might have implicated or exculpated Motassadeq. The reason for his reticence: the United States is holding bin al-Shibh and Mohammed as "enemy combatants" in a secret location. As then-Assistant Attorney General Michael Chertoff, who is now the nominee for director of the Department of Homeland Security, explained in a related case, allowing lawyers to depose enemy combatants would pose "immediate and irreparable harm" to U.S. national security.

The Motassadeq case illustrates a trans-Atlantic clash over how to combat terrorism. The United States approaches terrorism as a war and has detained nearly 600 men at Guantánamo with neither the rights of criminal suspects nor of prisoners of war. Unknown numbers of other detainees are held at U.S. bases around the world, and according to the National Strategy for Combating Terrorism , the war on terror will not return to the criminal domain until Al Qaeda has been reduced to an isolated, local, less lethal threat.

In Europe, by contrast, governments widely consider terrorism to be largely a law enforcement matter. Even when intelligence agencies like Britain's MI5 disrupt a terrorist cell, they are still required to treat detainees the way police treat suspects, so that detainee testimony remains valid in court.

This difference has added tension to a largely cooperative international relationship against terrorism. In several European cases, the difference between American interrogations of enemy combatants and European courtroom requirements could allow accused terrorists to go free.

Jonathan Winer, a top State Department antiterrorism official in the Clinton administration, faults both sides. "European concerns about civil liberties are incompatible with protecting people from terrorists," he said. "We need more sensitivity from civil liberties people that we're confronting very evil people. And we need more sensitivity from law enforcement that due process is needed. Extrajudicial processes are not the way to bring the rule of law to people threatened by terrorism."

+  From "complacent" to "overreacting"

Experts on both continents say the problem comes from the United States' rush to put together a counterterrorism strategy after 9/11. The biggest European countries started cracking down on terrorism in the 1970s, when nationalist and leftist groups were most active. The extra decades have given them time to adapt law enforcement and the courts to the extra demands of terrorism prosecutions.

In France, "a long tradition of internal subversion has created more tolerance for what we'd consider police state activities," according to Jeremy Shapiro, an expert in French counterterrorism at the Brookings Institution in Washington. He said police routinely listen in on mosques and have broad power to detain people without charge. "Before the 1998 soccer World Cup, they went downtown and rounded up the usual suspects. They just hold them for up to four days with no charge." In Britain, police can arrest anyone associated with a named terrorist group. In Spain, judges have far more power than in the United States, with the ability to hold people in detention for up to four years without charges and to direct investigations and police resources.

American law grew more strict in the 1990s, after the first World Trade Center bombing, the Unabomber and the Oklahoma City bombing. The 1996 antiterrorism law increased domestic surveillance and boosted law enforcement capabilities. According to Michael Scheuer, who from 1993 to 1996 led the CIA's task force tracking Osama bin Laden, the CIA began disrupting Al Qaeda cells abroad during the Clinton administration and transferring detainees to other countries. But within the United States, terrorists like the first World Trade Center bombers were tried in criminal court under heavy guard, rather than in the military tribunals currently in planning for Guantánamo detainees.

Before 9/11, the U.S. and Europe both viewed the other as complacent on terrorism. According to Dale Watson, former chief of the FBI's counterterrorism bureau in Washington D.C., the Europeans did not take the Al Qaeda threat as seriously as Hezbollah and domestic terrorist groups. European officials worried that the United States was too focused on civil liberties rather than crime fighting.

The initial reaction to 9/11 was tremendous international unity. Less than two weeks after the attacks, the U.N. Security Council passed Resolution 1373, a binding resolution requiring countries either to try terrorists or to extradite them. The U.N. created a committee to coordinate counterterrorism efforts around the world, led by Spanish diplomat and one-time hostage Javier Rupérez. He now travels the world, helping different countries harmonize laws to eliminate refuges for terrorists.

However, international tensions rose when the U.S. decided to pursue a military strategy towards terrorism. Shapiro, of the Brookings Institution, says before 9/11, "They viewed the U.S. as being complacent on this problem. And now they view us as overreacting."

Despite the complaints, since 2001, Europe has largely let the U.S. set the tone in the fight against terrorism. It has followed the American lead on the invasion of Afghanistan, the crackdown on terrorist financing, the tightened security over air travelers and cargo shipping, and the streamlined extradition processes.

Although each European country sets its own counterterrorism laws, the European Union created a post in 2004 that is similar to the U.S. director of homeland security. While lacking a budget and staff, the new director, Gies de Vries, is trying to unify laws in E.U. member states.

In 2004, ministers from throughout the European Union agreed on over 100 tactics for cracking down on terrorism. They vowed to create international arrest warrants, joint investigation teams, and unified laws against terrorist financing.

The European Union recently signed an extradition treaty with the United States -- the first time that body has crafted foreign policy on behalf of all its member states. The treaty speeds the process in return for the United States' agreement to drop capital charges against people extradited from Europe. Under European law, it is illegal to extradite anyone who might receive a death sentence.

+  "A Portent of Things to Come"

Although laws have been passed to enhance cooperation between the U.S. and Europe, in practice, the relationship continues to be strained. In Spain, one of Europe's most prominent counterterrorism officials, Judge Baltasar Garzón has led investigations into 9/11 and the Madrid train bombings. Garzón told FRONTLINE that his investigations have suffered because "there are evidentiary elements that have never arrived" from the United States.

Garzón has indicted Mohammed and bin al-Shibh, but cannot prosecute them while they are in American custody. He said that his court proceedings could only use testimony from witnesses and suspects who have been given access to lawyers. "That is the rule of law and those are the rules we abide by within the rule of law," he said.

Ex-CIA agent Michael Scheuer says Guantánamo is the result of a haphazard counterterrorism policy. He told FRONTLINE, "It's been a cobbled-together system by the clandestine service to execute its mission and it's not been well thought through in terms of the government as a whole."

However, according to Scheuer, "Law enforcement is never going to be the answer to this problem. We can't possibly arrest and convict enough of these people to put them in jail to solve the problem. But all times you can do it, it's a worthwhile thing to do, whether in the United States or Germany or Morocco."

Motassadeq, in Hamburg, is back on trial, facing renewed charges of complicity in mass murder for 9/11. London's Financial Times reported that Germany's interior and justice ministers visited Washington repeatedly in 2004 to convince the United States to let bin al-Shibh and Mohammed testify. The United States agreed to provide the defense with some exculpatory testimony from their interrogations, but refuses to provide the transcripts, the interrogators and the detainees themselves.

Motassadeq's case is expected to conclude in March, but Andreas Schulz, a lawyer representing the families of Sept. 11 victims in the case, expects that Motassadeq will get off on the charge of accessory to murder.

The tensions expressed in the Motassadeq case and by Judge Garzón in Spain are likely to continue. Scheuer, the ex-CIA agent, calls the frictions in the trans-Atlantic relationship "a portent of things to come regarding the whole security situation inside the European Community and the safety of the United States."

And, warns Scheuer, these tensions may have an unintended consequence: "Friction between Europe and United States," he says, "is something that certainly benefits Osama bin Laden, without a question."

Steven Bodzin reports from San Francisco. He conducted research for FRONTLINE's 2004 documentary, "The Jesus Factor," and has written for public radio, Wired News, and The New York Times Magazine.

+ Cops Across Borders: The Evolution of Transatlantic Law Enforcement and Judicial Cooperation This article, from the Council on Foreign Relations examines the "history of the political and technical development of the new transatlantic institutions prior to September 11, describes how they are being applied in the current security environment, and projects their likely further near-term evolution in light of that environment."