A South Carolina man executed last month by firing squad may have suffered for an extended period of time before dying because shooters largely missed his heart, an autopsy commissioned by the state shows.

Mikal Mahdi died on April 11 after being shot by a three-person firing squad. But an autopsy revealed two wounds on his chest, not three. None of the bullets hit his heart directly, as is supposed to happen during the execution. Instead, the wounds caused damage to his liver and other internal organs, and allowed his heart to keep beating. Pathologists say the injuries likely caused the prisoner pain and suffering while he was still conscious.

"He's not going to die instantaneously from this," said Dr. Carl Wigren, a forensic pathologist who reviewed the autopsy documents for NPR. "I think that it took him some time to bleed out."

On May 8, lawyers for Mahdi notified the South Carolina Supreme Court that the execution was "botched." They cited the state's autopsy and a forensic report that Mahdi's lawyers commissioned from another pathologist, Dr. Jonathan Arden.