By Jason Tomassini

BALTIMORE (Reuters) - A murder-for-hire trial that is the first to test Maryland's revised death penalty statute, seen as the most restrictive in the nation, begins with opening statements on Friday.

Walter Bishop Jr., 29, is accused of fatally shooting William Porter at a gas station Porter owned last year, a crime he is accused of committing at the behest of Porter's wife, Karla, who is awaiting her own murder trial, court records said.

Both Bishop and Karla Porter could face the death penalty if convicted, and Bishop's is the first death penalty trial since Maryland revised its statute two years ago, according to the Baltimore County State's Attorney's Office.

At the time, Democratic Governor Martin O'Malley was pushing to abolish the state's death penalty, but lawmakers nixed his proposal in favor of more restrictive measures, said Richard Dieter, executive director of the Washington, D.C.-based Death Penalty Information Center.

In order for prosecutors to seek the death penalty, the new statute requires DNA or video evidence linking the defendant to the crime or video of a voluntary interrogation and confession.

The evidence in this case includes video of Bishop confessing to police. But his attorneys said the confession was a result of entrapment and that the death penalty statute was "unconstitutionally vague" in defining what constitutes a voluntary video confession, court records show.

Baltimore County Circuit Court Judge Mickey Norman has already rejected several attempts to strike the death penalty in the case.

Bishop's public defenders could not be reached for comment, and the Baltimore County State's Attorney's Office declined comment until the trial is concluded.

The death penalty is legal in 34 states, although rules for imposing it differ. Five people have been executed in Maryland since the death penalty was reinstated in the United States in 1976, and five are currently on death row, according to the Death Penalty Information Center.

"In Maryland, there's this added requirement as to evidence," Dieter said, referring to the revised law, while in other states, "usually it's if the jury thinks it should be death, it should be death."

Illinois used to have one of the more restrictive death penalty laws, prohibiting it from being sought in cases based on testimony from jailhouse informants, until the death penalty was abolished earlier this year.

In 2005, Massachusetts Governor Mitt Romney pushed a bill to allow the death penalty if there was DNA evidence and the defendant was ruled guilty beyond any doubt, not just reasonable doubt. State lawmakers opted to keep the death penalty abolished.

(Editing by Ellen Wulfhorst and Cynthia Johnston)