A Texas man with an IQ of just 67 was executed on Thursday after the U.S. Supreme Court rejected arguments he was not mentally disabled, reported the Associated Press.

According to the Huffington Post, Robert Ladd, 57, was scheduled to die because of his 1996 conviction for the killing of 38-year-old East Texas native Vicki Ann Garner.

Although his attorneys have never contested his guilt, The American Civil Liberties Union has vigorously contended Ladd should not be put to death based on a high court precedent outlawing the death penalty for those who are deemed "intellectually disabled."

When he was just 13, the Texas Youth Commission declared Ladd "fairly obviously retarded." The ACLU also stresses the same psychiatrist who diagnosed Ladd back then still stands by his diagnosis, adding that he now states "three separate interviews confirmed mental retardation."

Just more than two decades ago, the nearby Andrews Center, which serves the intellectually handicapped, declared Ladd eligible for services.

Texas' actions mirror those taken by the state of Georgia earlier this month when state officials followed through with the execution of Warren Hill, a man whose lawyers also contended suffered from mental shortcomings.

"Texas and Georgia are two sides of the same coin," Brian Stull, Ladd's ACLU attorney, said in an email to The Huffington Post. "Both standards are non-scientific, violating a recent ruling by the Supreme Court in Hall v. Florida requiring science to control these determinations. Both tests pose grave risks of executing intellectually-disabled prisoners.

In recent times, states all across the country have begun enacting statutes stipulating that anyone with an IQ of less 70, or intellectually disabled, is not eligible for the death sentence.

Stull later told MSNBC.com "this case is indeed stranger than fiction. Anywhere else in the country, Mr. Ladd's IQ of 67 would have meant a life sentence, not death sentence. Robert Ladd's fate shouldn't depend on a novella."