Wilson’s lawyers failed to convince the courts he was mentally retarded and  therefore ineligible for the death penalty earlier this week.

During the appeal at the Supreme Court, his lawyers pointed to a psychological test carried out in 2004 that concluded he had an IQ of 61. The generally accepted minimum mental competency standard is 70.

But the claim was rejected on the grounds that it was based on a single test that could be faulty.

Wilson was convicted of murder in 2004 after shooting a police informant to death who had fingered Wilson as a drug dealer.

Wilson maintained his innocence until the end of his life, although his defence had hinged on his mental capabilities. According to reports, there was no forensic evidence or eyewitness testimony involved in the murder case, but rather an alleged accomplice and his wife testified against him.

In a statement, Texas assistant attorney general Edward Marshall said: “Wilson created schemes using a decoy to screen his thefts, hustled for jobs in the community, and orchestrated the execution of the snitch, demonstrating inventiveness, drive and leadership.”

The 54-year-old was declared dead at 6.27pm local time on Tuesday night.

Image: Getty