Ever since California added the death penalty to its penal code in the 1870s, supporters have argued that the threat of executions would make potential murderers think twice before committing heinous crimes.

The Bee made that argument numerous times in its early years, and many politicians and prosecutors have offered it since. But does the evidence show that capital punishment deters murders, even when applied frequently and expeditiously? Research suggests it does not.

One obvious way to look at the problem is to compare the murder rates in states with executions and those without.

For example, compare the homicide rates in California, New York and Texas, as the National Research Council has done. From 1974 to 2009, the homicide rates in those three states tracked virtually identically – going up at the same time in the late 1970s and late 1980s and all declining dramatically since then.

Yet during that time Texas had 447 executions and New York had none; California had 13. Clearly, something other than executions has had an effect on declining murder rates. And that clearly is what we should focus on.

That pattern holds up in comparisons of Canada and the United States, too.

Murder rates in Canada have gone up and down in virtual lockstep with U.S. rates over the years. Yet Canada has had no executions since 1962. In fact, during the period just after the United States reinstated the death penalty in 1976, murder rates remained high in the United States while declining in Canada.

Murder rates in the United States began a real decline in the 1990s, and research suggests multiple factors are involved.

For example, crime experts attribute the steep decline in violent crime that began in 1993 to new police strategies such as targeted police patrols of gun-crime hot spots and effective enforcement of gun laws. The waning of the crack epidemic and the decline of the percentage of 18- to 24-year-olds in the population also played a role.

In all the states, life imprisonment is used more often than death sentences in murder cases. That in itself may be a reason for the decline in murder rates – keeping the most dangerous killers out of society.

Is it really rational from a policy perspective to assume that the most heinous killers in American society respond to any punishment threat at all – whether execution or life in prison – as a deterrent? Would increasing the frequency of executions – or speeding up executions – make one iota of difference with these stone-cold killers? Highly unlikely.

The National Research Council conducted a review of more than three decades of research on the deterrence effect of the death penalty, releasing its 144-page report, "Deterrence and the Death Penalty" in April (see www.nap.edu). Its conclusion: The research to date is flawed and "not informative" about whether the death penalty has an effect on murder rates.

Therefore, the National Research Council concludes, "these studies should not be used to inform deliberations requiring judgments about the effect of the death penalty on homicide." Further, these studies "should not influence policy judgments about capital punishment."

The Bee in the early 1900s called for state-sanctioned public hangings, in part, because it believed that the death penalty would deter not only would-be murderers but the citizenry taking law into its own hands through lynchings.

With the death penalty, the logic went, the call to vigilantism would disappear.

The same logic, however, should apply to life sentences that take killers permanently out of society, where they no longer pose a danger to society and are punished for their crime. They die in prison. That won't satisfy those who want an "eye for an eye," retribution or revenge. But it does ensure a society based on law and order – as opposed to "hellish deeds rampant everywhere," in the words of The Bee in 1912, or vigilantism.

Those who support the death penalty and those who oppose it will hew to their positions regardless of the evidence on deterrence. In the end, it is our values that will have to decide the matter.