IN 1953, in Upper Heyford, England, an American named Clarice Covert killed her husband with an ax as he lay sleeping, then climbed into bed with his bloody corpse. The next day she confessed her terrible deed to a psychiatrist at the air base where her husband was stationed. She was quickly convicted of murder, not by a jury trial but by a U.S. court-martial.

Her crime might have been long forgotten. But the proceedings that followed her conviction — 50 years ago June 10 — established a significant legal principle that holds deep relevance today for the war on terror.

Covert's case, which had the distinction of being ruled on twice by the U.S. Supreme Court, upheld for the first time the principle that the Bill of Rights reaches beyond U.S. borders. The court ruled that just because Covert was tried abroad, she didn't forfeit her 6th Amendment right to a jury — and, more broadly, that the government does not enjoy unchecked power simply because the trial of an American is held overseas.

This principle is being put to the test today, most notably in the U.S. policy that dictates which suspected terrorists are held offshore in Guantanamo Bay, Cuba. It is because of Reid vs. Covert that the Bush administration has not detained any U.S. citizens there.

Now, the debate is moving to the next level. While the government argues that the precedent applies only to Americans, and therefore that it is free to detain and try foreigners without the protections of the Bill of Rights as long as it does so outside U.S. territory, others argue that the principle should be expanded. To remain true to the larger meaning of Reid vs. Covert, they argue, the Bill of Rights should be applied to foreigners as well. The Bill of Rights should restrain the federal government when it acts overseas against foreigners, just as it already restrains the U.S. government when it tries aliens at home. This would send an important signal that the U.S. lives by its Constitution, a document that balances the executive, the judiciary and the legislature and rejects unfettered executive power.

In the decades before Covert took an ax to her husband, overseas trials by the federal government were rare. But by the 1950s, the Cold War was well underway, and a massive and unprecedented number of American troops had been deployed around the world. With hundreds of thousands of dependents following these troops to such places as Britain, Japan and Germany, overseas trials of civilians became more common. Covert never disputed that she had killed her husband. Her appeal turned on whether the military could try a civilian for acts outside the battlefield. While courts-martial have an honorable tradition, they do not employ grand juries, nor the impartial jury guaranteed by the 6th Amendment.

The Eisenhower administration gave two reasons why Covert's court-martial was proper. First, Britain had agreed that, as part of the deployment of American troops, the U.S. would try those troops and their families for any crimes committed there. Second, and more significant, the U.S. government argued that Covert had no 6th Amendment right to a jury trial: "The Constitution does not go overseas." The idea that the Constitution's protections stop at the border dates back to the earliest years of the nation, and later legal decisions backed it up.

The high court initially agreed, ruling in 1956 that Covert's military trial was proper. But it did a surprising turnabout the next year, declaring, "We reject the idea that when the United States acts against citizens abroad, it can do so free of the Bill of the Rights." The shield of the Constitution, the justices stated in reversing a centuries-old legacy, cannot be ignored by the executive branch simply because the accused happens to be abroad. The federal government was, the court said, a creature of the Constitution; therefore, it had to act in accordance with the Constitution — wherever it acted. It does not matter if the prison or courtroom is leased from Cuba or located in South Carolina.

Adhering to this principle even more broadly — and applying those constitutional protections to foreigners being held anywhere by the U.S. government — would not dramatically change the fundamentals of our terrorist detention policy. Enemy combatants could be held and tried by military authorities whether they were in California or Cuba; the law of war applies in both places.

What it would do, however, is permit the courts to play a more active role in ensuring that innocent individuals were freed. And it would prevent the president from doing an end-run around the Constitution by acting in a foreign country because the Bill of Rights applies to any foreign citizen arrested and tried on U.S. soil.

For example, an individual mistakenly detained by the U.S. military abroad could challenge his detention through the ancient right of habeas corpus. Today, that is true only if he is detained on American soil. This creates an incentive to use offshore facilities — which is exactly what the Bush administration did in creating the Guantanamo prison camp.

The deeper principle announced by the U.S. Supreme Court half a century ago in Clarice Covert's case is that ours is a system of checks and balances that abhors unrestrained executive power. It is a distinguishing feature of our political tradition — and a source of our enduring strength as a nation.