Those who believe that deterrence justifies the execution of certain offenders bear the burden of proving that the death penalty is a deterrent. The overwhelming conclusion from years of deterrence studies is that the death penalty is, at best, no more of a deterrent than a sentence of life in prison. The Ehrlich studies have been widely discredited. In fact, some criminologists, such as William Bowers of Northeastern University, maintain that the death penalty has the opposite effect: that is, society is brutalized by the use of the death penalty, and this increases the likelihood of more murder. Even most supporters of the death penalty now place little or no weight on deterrence as a serious justification for its continued use.
States in the United States that do not employ the death penalty generally have lower murder rates than states that do. The same is true when the U.S. is compared to countries similar to it. The U.S., with the death penalty, has a higher murder rate than the countries of Europe or Canada, which do not use the death penalty.
The death penalty is not a deterrent because most people who commit murders either do not expect to be caught or do not carefully weigh the differences between a possible execution and life in prison before they act. Frequently, murders are committed in moments of passion or anger, or by criminals who are substance abusers and acted impulsively. As someone who presided over many of Texas's executions, former Texas Attorney General Jim Mattox has remarked, "It is my own experience that those executed in Texas were not deterred by the existence of the death penalty law. I think in most cases you'll find that the murder was committed under severe drug and alcohol abuse."
There is no conclusive proof that the death penalty acts as a better deterrent than the threat of life imprisonment. A 2012 report released by the prestigious National Research Council of the National Academies and based on a review of more than three decades of research, concluded that studies claiming a deterrent effect on murder rates from the death penalty are fundamentally flawed. A survey of the former and present presidents of the country's top academic criminological societies found that 84% of these experts rejected the notion that research had demonstrated any deterrent effect from the death penalty .
Once in prison, those serving life sentences often settle into a routine and are less of a threat to commit violence than other prisoners. Moreover, most states now have a sentence of life without parole. Prisoners who are given this sentence will never be released. Thus, the safety of society can be assured without using the death penalty.