Do you still get your ideas about American crime from American cop shows? If so, your ideas may be a little out of date. Over the past decade, American cities have become suddenly and dramatically safer.

Between 1995 and 2005, the number of murders in the United States dropped from nearly 25,000 a year to under 15,000. An American was less likely to be murdered in 2005 than in 1960. And the total rate of criminal victimisation tumbled to its lowest level since records began in 1974.

It would be rash to credit the death penalty alone for this triumph. But it would equally be wrong to deny capital punishment its share of the credit.

When crime is punished lightly, criminals feel empowered--and crime proliferates. In the 1960s, for example, US courts placed new restrictions on police, raised new barriers to criminal prosecution, and shortened sentences for the convicted. As crime rates surged between 1960 and 1969, the number of prisoners actually declined.

It was as if the US had decriminalised crime. What happened next has been described by one American writer as “the great havoc”: a collapse of order that ravaged once great cities like Detroit and exacted widespread economic and social costs. In 1974, one US household out of three said it was a victim of crime, and crime eclipsed inflation, unemployment, Vietnam and Watergate as the number one concern of American voters.

 In a democracy, the number one concern of voters gets attention. Aggressive politicians, especially Republicans, began to run for office promising action on crime: more police, tougher sentences--and the return of the death penalty. In 1974, the Supreme Court effectively overturned a 1972 decision against the death penalty and soon the worst offenders were being sentenced to die. The first of the “new” death sentences was carried out in 1977 in Utah.

Yet while execution was often sought after 1974, for nearly two decades it was rarely imposed. Procedural delays and manoeuvring by lawyers extended stays on death row from six, to nine, to a peak of 11 years.

And through it all, public opinion in favour of the death penalty intensified--and with it, the swing to the political right. By 1994, nearly 80% of Americans supported the death penalty. That year the Republicans recaptured both houses of Congress from the Democrats for the first time since 1952. The year before, the Republican Rudolph Giuliani won the mayoralty of New York on a get-tough-on-crime platform. Giuliani supported the death penalty. So did the Republican governor of New York, George Pataki. In 1995, New York would become the 38th state to restore its death penalty. In 1994, the number of executions rose above 20 a year for the first time. Perhaps not coincidentally, 1994 was also the year in which US crime rates--led by those of New York City--began to turn dramatically and decisively down.

It would be an exaggeration to credit the death penalty alone for the improvement. In the two decades since 1974, more than 400,000 Americans have been murdered--and barely 1000 of their killers have been executed. In no year since the restoration of the death penalty has the number of Americans executed exceeded the number killed by lightning.

So rare a punishment cannot qualify as a deterrent. Nor can it function as a tool of ultimate justice. Many horrendous murderers escape execution.

What the death penalty does do, however, is express as forcefully as society can--both to criminals and law-abiding citizens--that the authorities take crime seriously. It is not a substitute for all the other tools needed to defeat crime: more police and patrols, stricter laws, longer sentences and better economic opportunities.

If societies want to wind back crime, however, they need to begin by sending a clear message that the sheriff is back in town--that crime won’t be tolerated and will be punished to the full extent of the law. And nothing broadcasts that message like restoration of the most extreme punishment.

It is striking that Britain has imported many of the best US crime-fighting methods (but not the death penalty), only to see its rates of crime and violence continue to deteriorate. On some level, the bad guys don’t yet take the law seriously.

And as a society becomes safer, it can afford to again rediscover some leniency. Support for the death penalty has begun to decline again in the US. The number of executions is beginning to trend down. Yet crime levels remain low and continue to decline further: New York is now very nearly the safest 100,000-plus city in the US and probably one of the safest big cities in the world.

Restore the death penalty, and you restore safety. Restore safety, and everything becomes possible. Refuse the death penalty, and the job of reimposing legal order becomes much more difficult: citizens live in fear, trust in authority and law fade.

There may be another way of protecting society. But why ignore success?

David Frum is a resident fellow at AEI.