Authorities in Texas last night executed a prisoner despite protests from human rights groups that said he was mentally disabled.

54-year-old Marvin Wilson was condemned to death for a killing a police informant in 1992.

The US Supreme Court rejected a final appeal from defence lawyers in the hours before the execution.

Amnesty International called the decision “highly disturbing” and several other rights groups criticised the sentence.

In 2004 Wilson was diagnosed with mild mental retardation with an IQ of 61 which is well below the average for his age.

He was sentenced to death in April 1994.

Wilson had challenged his execution as unconstitutional under a 2002 Supreme Court ruling that banned executing mentally retarded people but gave States some discretion in deciding who qualified for protection.

“The application for stay of execution of sentence of death presented to Justice Scalia and by him referred to the Court is denied” the court said in an order earlier yesterday evening.

“Y’all do understand that I came here a sinner and leaving a saint” Wilson said as part of his final statement.

Texas has conducted roughly 3 out of every 8 executions since 1976 when the Supreme Court allowed the practice to resume after a 4-year break according to the Death Penalty Information Centre.

Wilson was the 7th inmate executed in Texas this year and the 25th executed in the United States in 2012.