A Georgia man has been executed for the 1995 killing of a sheriff’s deputy, who was slain minutes after a convenience store robbery.

Authorities said 49-year-old Robert Wayne Holsey was declared dead at 10.51pm on Tuesday at the state prison in Jackson.

Holsey was represented at his murder trial by an alcoholic lawyer who was under investigation at the time for stealing from a client and who drank a quart of vodka every night of the trial.

He was sentenced to death for the 1995 murder of a police officer. The Georgia supreme court refused to stay the execution and the US supreme court also declined to intervene.

Even in a capital system that has seen its fair share of incompetent and negligent legal representation, the story of Holsey’s 1997 trial stands out as particularly egregious. His attorney, Andy Prince, had a history of heavy drinking since the age of 14.

Every night during the trial he drank the equivalent of more than 20 shots of vodka. He was also under police investigation at the time for having stolen more than $100,000 from a client – a theft for which he was convicted soon after Holsey’s trial ended, sentenced to 10 years in prison and disbarred from practising the law.

As a further indication of his mind not being entirely focused on Holsey’s life-and-death legal struggle, shortly before trial Price was arrested for disorderly conduct and accused of threatening to shoot three black neighbours to whom he was shouting racial slurs. Price was white and his capital client defendant black.

A while after Holsey was put on death row, Price, who died in 2011, was himself released from prison. By then sober, he told a 2006 court hearing that he “shouldn’t have been representing anybody in any case” at the time of the Holsey proceedings.

Holsey’s current lawyer, Brian Kammer, has argued that Price’s alcohol-sodden incompetence was not merely academic – it effectively put Holsey on death row. A key piece of information about Holsey, that should have been emphasised at the sentencing phase of his trial, was that he was intellectually disabled with a level of functioning equivalent to a nine-year-old.

His intellectual difficulties were well recorded through his school career and in his record of youth detention and adult custody. Yet Price told the trial jury that intellectual disability, or mental retardation as it was then known, was not a factor in the case.

Instead of pressing the jury at the sentencing stage of the trial – at which the 12 members of the public decided whether or not to sentence Holsey to death – to take into account the defendant’s brutal childhood and history of intellectual disabilities, the lawyer in fact handed over the case to a junior attorney who had never tried a death penalty case. The new lawyer was thrown into the deep end, entirely unprepared to argue that Holsey’s life should be spared.

The US supreme court has previously ruled that it is unconstitutional to execute a prisoner with what is still called mental retardation in legal circles. It has also ruled separately that any defendant is constitutionally entitled to effective assistance of legal counsel.