An inmate put to death last month in South Carolina’s second firing squad execution was conscious and likely in extreme pain for up to a minute after the bullets missed their target, attorneys allege.

Dr. Jonathan Arden, a forensic pathologist hired by Mikal Mahdi’s attorneys, alleged that the execution on April 11 was a “massive botch” after he completed an analysis of the autopsy findings, according to the pathologist’s report, which was filed Thursday with a letter to the state Supreme Court.

The lawsuit challenges the legal precedent set in Owens v. Stirling—that firing squads are humane if properly carried out—by alleging that Mahdi’s execution amounted to “cruel and unusual punishment” in violation of the Eighth Amendment.

Mahdi, 42, was convicted in the 2004 killings of an off-duty police officer in Calhoun County, South Carolina, and a convenience store clerk in Winston-Salem, North Carolina. He was sentenced to death for the murder of the officer and life in prison for the clerk’s murder. 

Arden called that virtually unheard of in his 40 years of examining bodies and said Marcus told him in a conversation that the possibility was remote.

The autopsy found damage in only one of the four chambers of Mahdi’s heart — the right ventricle. There was extensive damage to his liver and pancreas as the bullets continued down.

“The entrance wounds were at the lowest area of the chest, just above the border with the abdomen, which is an area not largely overlying the heart,” Arden wrote.

Orangeburg Department of Public Safety Capt. James Myers, 56, was violently murdered by Mikal Mahdi on July 18, 2004, at a shed on his property.  (SC Law Enforcement Officers Hall of Fame)

Mahdi was sentenced to death in 2006 after he admitted to killing off-duty Orangeburg Department of Public Safety Capt. James Myers, 56, on his property on July 18, 2004. 

Myers had been shot at least eight times and his body was burned when his wife found him in their shed, which was near a gas station where Mahdi attempted to purchase gas with a stolen credit card. He left a vehicle he had carjacked in Columbia at the gas station and was later arrested in Florida while driving Myers’ unmarked police truck.

Mahdi also admitted to murdering convenience clerk Christopher Boggs three days before he killed Myers. Boggs was shot in the head twice while checking Mahdi’s ID, according to The AP.

The Associated Press contributed to this report.