A former Florida prison governor turned campaigner against capital punishment has revealed the horrific and disturbing details of a botched execution in 1997 that effectively "burned him alive" and caused his head to explode.

The ex-Florida State Prison official, Ron McAndrew, described the death of Pedro Medina, whose body was scorched by a malfunctioning electric chair that left the smell of his remains lingering for weeks following his execution on 27 March of that year. Today, McAndrew campaigns vigorously against the death penalty and pushes for its eradication.

"We didn't execute him – we burned him alive," McAndrew said of Medina's death, which occurred while he was overseeing the correctional facility.

The 87 year old recalled the nightmare he witnessed as a condemned prisoner went through his final moments while prison staff looked on as his body caught fire on a wooden electric chair known as "Old Sparky."

It stands as one of the most harrowing and distressing execution failures in American history.

"He caught fire. His body was twisting, and he was fighting the straps," the former governor told the Daily Mail, explaining that "Old Sparky" began pumping 2,000 volts of electricity through Medina's body.

"It was obvious he was still alive when his head was on fire. It was a horrible way to kill somebody."

He described vivid blue and orange flames erupting from the side of Medina's head as he perished inside the execution chamber, situated roughly 47 miles southeast of Jacksonville. Medina thrashed violently back and forth in the chair and clenched his fists as the flames took a full four minutes to claim his life.

McAndrew stood and watched as the convicted killer uttered his final words while engulfed in flames: "I am still innocent."

Medina, who had been convicted of murdering an elementary school teacher who lived next door to him in 1982, was 39-years-old at the time of his death.

A court found he stabbed her repeatedly and left her to bleed out in her Orlando flat before fleeing the scene in her car.

Officers were said to have later discovered Medina behind the wheel of the victim's vehicle.

McAndrew has consistently maintained that no crime — including a brutal murder and act of grand theft auto — could ever justify the sheer agony that officials inflicted upon the inmate.

The faulty electric chair, first used in 1923, had previously been used to execute 239 others, among them notorious serial killer Ted Bundy. "Old Sparky" was decommissioned following Medina's death, its 240th execution.