Death row inmate maintains innocence with disturbing final words before execution for heinous crimes

A death row inmate had some haunting final words as he maintained his innocence before being executed.

David Joseph Pittman has been on death row for more than 30 years and was put to death yesterday (September 17), marking the 12th execution in Florida this year.

Pittman, 63, died by lethal injection and was sentenced to death in the early 1990s for the murder of his ex's parents, Clarence and Barbara Knowles, and their 20-year-old daughter, Bonnie.

The three were stabbed in their home in the middle of the night, and their house was then set on fire.

He's said to have killed the family members because he was jaded about Clarence and Barbara's daughter filing for divorce from him.

While Pittman was charged for their murders, he has always maintained his innocence and insisted he didn't do it - something he reiterated in his final words.

The death row inmate died by lethal injection this week (Getty Stock Image)

He said before being put to death: "I know you all came to watch an innocent man be murdered by the State of Florida. I am innocent. I didn’t kill anybody. That’s it."

Prior to his execution, Pittman's legal team had argued that he was too intellectually disabled to be executed under the US Constitution.

"The State of Florida runs the imminent risk of executing an intellectually disabled person, contrary to the provisions of the Eighth Amendment," his attorneys wrote, as per USA Today.

The case was centered on the fact that Pittman reportedly had an IQ of 70 which, according to the American Psychiatric Assosication, means he may have been Intellectually Disabled.

"Traditionally, cognitive or intellectual functioning has been measured through the intelligence quotient (IQ) tests, with an IQ of less than 70 recommended for a clinical diagnosis of Intellectual Disability," the association explains on its website.

David Joseph Pittman was convicted of the murders of 3 people (Florida Department of Correction)

Elsewhere, the American Association on Intellectual and Developmental Disabilities states: "One way to measure intellectual functioning is an IQ test. Generally, an IQ test score of around 70 or as high as 75 indicates a significant limitation in intellectual functioning."

A judge dismissed Pittman's attorney's efforts, however, and argued that the convicted criminal planned the murders.

The Florida Attorney General's Office said: "The record shows that Pittman methodically planned the murders. He cut the telephone lines before entering the house in the middle of the night, stabbed and killed all three victims, and then set fire to the residence."

It continued: "In short, any claim that Pittman is intellectually disabled would run headlong into strong evidence of adaptive function."