Oklahoma is preparing to execute a man for his role in a quadruple slaying in Oklahoma City in 2005. Thirty-five-year-old Gilbert Ray Postelle is scheduled to receive a lethal injection Thursday morning at the Oklahoma State Penitentiary in McAlester. It will be Oklahoma's fourth execution since October, when the state resumed lethal injections following a nearly seven-year hiatus. During a clemency hearing last year, Postelle did not deny his involvement in the Memorial Day 2005 shooting deaths of James Alderson, Terry Smith, Donnie Swindle and Amy Wright. But Postelle's attorney argued that his client was learning disabled and suffered from years of methamphetamine abuse that began around age 12.