The Oklahoma Pardon and Parole board has denied a convicted murderer's request to commute his death sentence to life in prison.

The board voted 4-1 on Friday to deny clemency for 38-year-old Clayton Lockett, who refused to appear at the hearing.

Lockett is scheduled to be executed March 20 for the 1999 killing of 19-year-old Stephanie Nieman near Tonkawa.

Authorities say Lockett shot Nieman twice and then watched as 1 of his 2 accomplices buried her alive. The 2 co-defendants are serving life sentences.

Lockett and another Oklahoma inmate are suing to stop the state from killing them until the Department of Corrections discloses the origins of the drugs it plans to use in their executions.

Source: Associated Press, Feb. 28, 2014