Ronald Gray, a serial rapist and murderer on military death row, has lost his appeal to have his death sentence vacated.

Gray, formerly an Army cook, was convicted in 1988 of murdering two women and raping a third woman, and he was sentenced to death, NBC News reported on Thursday. He pleaded guilty to killing two other women in 1986 and 1987 among crimes committed on and near Fort Bragg, North Carolina, and received a life sentence related to those killings, the report said.

In his petition to the Army Court of Appeals, Gray claimed he was incompetent to stand trial, he was denied due process, the death penalty is racially biased and other objections. The decision against his appeal was unanimous, The Fayetteville Observer reported Wednesday.

"Pvt. Gray now has 30 days to file for reconsideration with the court or, alternatively, 20 days to petition for review at the next appellate level, the Court of Appeals for the Armed Forces," the Army said in a statement.

Gray, now 51, could be the first inmate put to death by the military since 1961. He has been confined at the U.S. Army Disciplinary Barracks at Fort Leavenworth, Kansas.