BY THE GRACE of state Sen. Thomas V. Mike Miller (D-Calvert), Maryland Gov. Martin O’Malley (D) has been handed a second chance — probably his last — to abolish the state’s death penalty. He should seize it.

Four years ago, in deference to Mr. O’Malley, who opposes capital punishment, Mr. Miller, the powerful president of the Senate and a supporter of the death penalty, allowed the issue to reach the Senate floor. There, despite cajoling, the governor could not corral the 24 votes needed for abolition. Instead, a bill was enacted that limited Maryland’s death penalty to cases where there is DNA evidence, a videotaped confession or a video linking the suspect to a murder.

Now Mr. Miller has given Mr. O’Malley a green light to try again — if he can find the necessary 24 votes in the Senate.

The good news is that the votes may be within reach. (They’re already there in the House of Delegates, according to nose-counters in Annapolis.) The puzzling news is that Mr. O’Malley, though he remains as opposed to capital punishment as ever, is balking.

Perhaps the governor is simply being cautious. According to The Post’s John Wagner, 23 senators are firmly, or relatively firmly, on record as prepared to end capital punishment, and several others are on the fence. But an excess of gubernatorial caution would be a mistake. Without a push by Mr. O’Malley himself, the status quo will remain unchanged and Maryland's death penalty will remain on the books.

In practice, it is in remission, having been suspended by a ruling from the state’s high court in 2006. Although five prisoners remain on death row, Maryland hasn’t executed anyone since 2005.

But even if the machinery of death is frozen, there are good reasons to abolish it for good and to eliminate a costly, unjust and dysfunctional system. In fact, the legislation four years ago codified an even more arbitrary system where the nature of the evidence, rather than the barbarity of the crime, is the crucial factor.

What’s more, the fundamental flaws in the death penalty’s application remain unresolved, including disparities based on race and jurisdiction. And there is no evidence proving that it is more effective at deterring homicides than is a sentence of life without parole.

Those flaws, as well as the steady drip of capital convictions overturned by DNA evidence, have prompted other states to use the death penalty more sparingly or to ban it altogether. Last year, according to the Death Penalty Information Center, 43 people were put to death, less than half the number executed in 1999 and the fewest in two decades.

Even more encouraging, just 77 convicts were sentenced to death last year, 75 percent fewer than 1996’s record total. Virginia, once a major death-penalty state, executed no one and imposed no death sentences. Today, the death penalty is either forbidden or in abeyance — meaning no one executed in the past five years — in 30 states.

The arguments against capital punishment are refreshed and strengthened every time a capital conviction is overturned. In September, Damon Thibodeaux was freed after 15 years on Louisiana’s death row — the 18th convict released from prison after analysis of DNA evidence. As long as the death penalty exists, the nation risks committing the gravest of injustices: killing innocent people.