O'Malley says punishment does not prevent violent crime as state bids to become 18th in union to abolish death penalty

The governor of Maryland, Martin O'Malley, has announced that he will seek to repeal the death penalty, in a move that would make his state the sixth in as many years to discard the ultimate punishment.

At the start of his final term as governor, that ends in 2016, O'Malley said he would use the full weight of his office to see the abrogation of capital punishment in Maryland. "The death penalty does not work in terms of preventing violent crime," he said.

This is the second time that O'Malley has attempted to repeal capital punishment in his state. In 2009 the effort was foiled when an abolition bill got stuck in committee, though this time supporters of repeal say they will force a full referendum should legislators attempt to block the reform again.

Maryland is a relatively small state with fewer than 6 million people, but how it handles the death penalty debate in the coming weeks will be closely watched, given its proximity to Washington and to the south, where most executions are now carried out. Should abolition be achieved this year, Maryland would become the sixth state in six years to throw out capital punishment, joining Connecticut, Illinois, New Jersey, New Mexico and New York.

Last year, Connecticut became the 17th state to abolish the death penalty. Among the 33 remaining that still have the punishment on their books, the actual practice of executions has receded to a rump of largely southern states; in 2012 most executions were confined to four states – Texas, which carried out 13 executions, followed by Arizona, Oklahoma and Mississippi on six each.

The call for repeal is also likely to be influential given O'Malley's prominent standing within the Democratic party. "O'Malley is a national figure, and he points to where Democratic policies are moving in future," said Richard Dieter of the Death Penalty Information Center.

Brian Evans of Amnesty International praised O'Malley for taking a courageous stance. "Support for the death penalty is waning in the US as people come to recognize that executions are a costly and ineffective deterrent to crime."

Witness to Innocence, a national group formed by exonerated death row survivors, pointed out that 142 men and women have been released from death sentences having been found to be innocent. "As long as the death penalty exists, innocent lives will continue to be at stake," the group said in a statement.