COLUMBIA, S.C. – South Carolina’s highest court on Monday rejected the last major appeal from Mikal Mahdi, who is scheduled to die by firing squad later this week for the ambush killing of an off-duty police officer.

Mahdi’s lawyers said his original attorneys put on a shallow case trying to spare his life that didn’t call on relatives, teachers or people who knew him and ignored the impact of weeks spent in solitary confinement in prison as a teen.

But the state Supreme Court, in a unanimous decision, ruled that many of those arguments were made in earlier unsuccessful appeals and refused to stop Friday’s scheduled execution so further hearings could be held.

Mahdi, who admitted killing an off-duty police officer in an ambush at the officer’s Calhoun County shed, is the fifth person set to be executed in South Carolina in less than eight months. All made final appeals to the state Supreme Court but all were rejected.

Mahdi has one more opportunity to live, by asking Republican Gov. Henry McMaster to reduce his sentence to life in prison without parole just minutes before his scheduled execution time. He is to be put to death with three bullets to the heart at 6 p.m. on April 11 at the Broad River Correctional Institution in Columbia.

But no South Carolina governor has offered clemency in the 47 executions carried out in the state since the death penalty resumed in the U.S. in 1976.

Mahdi, 41, was convicted of killing Orangeburg Public Safety officer James Myers in 2004, shooting him at least eight times, then burning his body. Myers’ wife found him in the shed, which had been the backdrop to their wedding 15 months earlier.

Myers’ shed was a short distance through the woods from a gas station where Mahdi tried but failed to buy gas with a stolen credit card and left behind a vehicle he had carjacked in Columbia. Mahdi was arrested afterward in Florida while driving Myers’ unmarked police pickup truck.

Mahdi also admitted to the killing three days earlier of Christopher Biggs, a Winston-Salem, North Carolina, convenience store clerk who was shot twice in the head as he checked Mahdi’s ID. Mahdi was sentenced to life in prison for that killing.

Mahdi pleaded guilty to killing Myers, leaving a judge under South Carolina law to decide if he would be sentenced to death or life without parole.

Prosecutors called 28 witnesses for Circuit Court Judge Clifton Newman to hear. The defense called two, according to Mahdi’s appeal.

The defense’s case to spare Mahdi’s life lasted only about 30 minutes. It “didn’t even span the length of a Law & Order episode, and was just as superficial,” Mahdi’s lawyers wrote.

Prosecutors said Mahdi was able to present much more evidence during a 2011 appeal that had to be heard inside a prison because Mahdi had stabbed a death row guard during an escape attempt. A judge rejected the appeal.

“In Mahdi’s vernacular, if his mitigation presentation before Judge Newman ‘didn’t even span the length of a Law & Order episode,’ the review of any potential error is in its 24th season,” the state Attorney General’s Office wrote in court papers.

As a prisoner, Mahdi has been caught three times with tools he could have used to escape, including a piece of sharpened metal that could be used as a knife, according to prison records. While he was on death row, he stabbed a guard and hit another worker with a concrete block, the records show.

“The nature of the man is violence,” prosecutors wrote.

Mahdi is to be the second inmate executed by South Carolina’s new firing squad after Brad Sigmon chose that way to die last month.

The firing squad is an execution method with a long and violent history in the U.S. and around the world. Death in a hail of bullets has been used to punish mutinies and desertion in armies, as frontier justice in America’s Old West and as a tool of terror and political repression in the former Soviet Union and Nazi Germany.

Before Sigmon’s execution last month, only three other prisoners in the U.S. had been executed by firing squad in the past 50 years. All were in Utah, most recently Ronnie Lee Gardner in 2010.

Three prison employees who volunteer for the role will fire high-powered rifles at Mahdi from 15 feet (about 4.5 meters) away, aiming for a target on his heart.

Mahdi also could have chosen the electric chair or lethal injection.