Anti-death penalty forces have gained momentum in the past few years, with a moratorium in Illinois, court disputes over lethal injection in more than half a dozen US states and progress toward outright abolishment in New Jersey.

The steady drumbeat of DNA exonerations - pointing out flaws in the justice system - has weighed against capital punishment. The moral opposition is loud, too, echoed in Europe and the rest of the industrialized world, where all but a few countries banned executions years ago.

What gets little notice, however, is a series of academic studies over the past half a dozen years that claim to settle a once hotly debated argument - whether the death penalty acts as a deterrent to murder. The analyses say yes. They count between three and 18 lives that would be saved by the execution of each convicted killer.