Philippine legislators recently abolished capital punishment for a wide variety of crimes while the states of Oklahoma and South Carolina broadened their range of capital offenses. Canadians have been dead-set against the death penalty for decades - this might explain why they call their soldiers "peacekeepers."
Threat of the death penalty has not been much of a deterrent to say, murder. The concept has introduced gradations of murder into one legal system. First degree, second degree, manslaughter, criminal negligence causing death - capital or non-capital.
Lawyers for even self-confessed killers work very hard to have their clients convicted of lesser charges, a life sentence being seen as a comparative break in some cases. The clients were variously drunk, abused as children, walked in their sleep, juggled multiple personalities, were coerced into confession by police, or-that old chestnut-they didn't know the gun was loaded. Maybe so, but the victim is still dead.