THE DEATH Penalty Information Center’s annual report on capital punishment is in, and even though it documents no dramatic developments in 2013, it confirms that death sentences and executions remain at or near historically low levels since the Supreme Court’s reinstatement of the death penalty in 1976. The death-row population has declined from its peak of 3,593 in 2000 to 3,108 this year, according to calculations by the NAACP Legal Defense and Educational Fund — and two states that rarely carry out executions, California and Pennsylvania, account for nearly a third of those condemned prisoners. Clearly, the death penalty is dwindling in the United States.

Five of those awaiting execution are in Maryland, which this year abolished the sentence of capital punishment. It seems worse than strange that these men should remain on death row, given that they were all convicted under a system that the legislature and Gov. Martin O’Malley (D) have repudiated on moral and practical grounds. Mr. O’Malley should make a New Year’s resolution to commute these last death sentences to life in prison, as he is authorized to do under Maryland’s constitution.

The Death Penalty Information Center and other capital-punishment foes attribute the death penalty’s decline to waning public support amid concerns about possibly innocent defendants on death row and other flaws in the system. This is part of the story, but the decline in capital punishment also reflects the decline in commissions of the crime for which it is most often imposed: murder. The national murder rate in 2012, 4.7 per 100,000 population, was among the lowest recorded since 1963. Fewer murder cases mean fewer potential death sentences. In a safer society, there is less of the fear that often drives demand for harsh punishments. The rate at which U.S. juries sentence defendants to death has fallen from its post-1976 peak of 17.8 per 1,000 murders, in 1999, to 5.1 per 1,000 murders in 2013 — a 71 percent decline. Meanwhile, the murder rate dropped 25 percent during that time.

Supporters and opponents of capital punishment alike have reason to applaud the remarkable reductions in homicide, and other violent crime, that this country and its law enforcement agencies have achieved in the past quarter-century. Preliminary estimates from such cities as Chicago and Philadelphia, which are on course to record the fewest homicides this year since 1965 and 1967, respectively, suggest that 2013 brought further progress.

Still, the reasons for violent crime’s extended decline are not well understood — and the fact that the 2012 national murder rate was unchanged from 2011’s implies that the years of rapid improvement may be ending. Though much rarer than it was in the recent past, violent crime remains far more common in the United States than in other advanced industrial countries. Though they have certainly earned their laurels, this country’s increasingly effective crime fighters dare not rest on them.