The bombshell photofit evidence that shows Carlton Gary cannot be the 'Stocking Strangler': DAVID ROSE's 19-year fight to save an American man from execution for sexually driven serial murders he did not commit

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A year ago this week, Robert Grubbs, a retired deputy sheriff in the US city of Columbus, Georgia, called his former boss to say he had made an unusual discovery. Helping his mother-in-law clean out her attic, he had found an old, plastic briefcase containing what looked like sensitive documents.

It had belonged to an investigator working on the case of the 'Stocking Strangler', a sexually driven serial killer who terrorised elderly women in an affluent, all-white neighbourhood in the city in the late 1970s. He killed them with their own stockings, using an unusual knot.

One of the documents from the attic immediately caught Grubbs's eye: a police artist's sketch of the killer, drawn at the time of the manhunt in consultation with Gertrude Miller, the only one of eight women the monster raped who had survived.

The police had supposedly caught the strangler in 1984, more than six years after the final murder, and at his trial in 1986 the suspect was convicted and sentenced to death.

Carlton Gary was convicted of the murder and rape of seven elderly women in Columbus, Georgia

At its dramatic climax, Ms Miller, then 73, told the jury she was certain that the defendant, Carlton Gary, was the man who raped, beat and strangled her.

Yet the sketch discovered in the attic looked nothing like Carlton Gary. It depicted a man with a large, square chin and distinctive lines of scars on his neck – features that Gary does not have.

After it was drawn in 1977, the police considered it a valuable investigative tool and showed it to dozens of possible witnesses. Yet when it came to the trial, the sketch was concealed. If not for deputy sheriff Grubbs, it would have stayed buried for ever. This alone is compelling evidence that Ms Miller had identified the wrong man – but it is not the only sticking point.

Ms Miller only told police that her attacker was Gary after seeing him on television, already named as the strangler and flanked by the cops who arrested him.

And then there is the forensic evidence. Analysis of the nightdress she was wearing on the night she was raped revealed two stains containing sperm cells, both from the same man. DNA tests have confirmed with absolute certainty that their source was not Gary.

Last week, over two intense days in the same Columbus courthouse where the case was originally tried, I attended the final hearings of Gary's last-ditch appeal against execution. Four decades after it was made, the sketch took centre stage: the last addition to a mountain of fresh evidence attesting to Gary's innocence.

For me, the appeal was the latest stage of a very long saga. I made the first of many visits to Columbus in May 1996, and have been working actively on Gary's case since 1998, writing many articles and a book.

For the past 16 years, I have also been the official – though unpaid – investigator for Gary's defence team, led by Atlanta attorney Jack Martin. I accepted the position because I decided that with a man's life at stake, it would be wrong as an investigative journalist not to hand over evidence I discovered immediately.

So I sat next to Gary, 67, at the defence table – as his wife Debra and their adopted daughter Charity looked on – and Martin made his last, passionate plea to Judge Frank Jordan to spare his client's life.

Victim Gertrude Miller, who was raped but survived, helped police produce this photofit of her attacker, which has not been seen until now

Gary was not in great shape. When he arrived, he had not had a shower for three months because there had been no hot water in the prison death row blocks. There was, he said, no heating either, and a gap in the glass of his barred cell window let the wind blow straight in.

Last year, Georgia executed nine prisoners, more than any other state in the US. Gary said: 'When they take someone else to murder them, we all get depressed, and I knew some of those guys real well.'

When I first met Gary in 1998, he was allowed out of his cell most of the day. He had access to art materials – he is a skilled painter, and once made crochet dolls as Christmas presents for my daughters. Now that has been taken away, and he spends most days confined to his cell, the size of a king-size bed.

In the oak-panelled courtroom, the tension was palpable: after all there is a lot riding on the Gary case.

Columbus is a quintessential city of America's Deep South, where a few white families have dominated politics and the legal system for many decades – the 'good ole boy network', some of whose members graduated from the Gary case to positions of power and influence. For them, the quashing of Gary's conviction, or even the commutation of his sentence, would represent humiliating defeat.

In earlier times, Columbus was scarred by lynchings and was a base for the Ku Klux Klan. There are direct links between those times and the Gary case. For example, 1956 saw the assassination of Dr Thomas H. Brewer, a black civil rights leader, in front of numerous witnesses. His killer went unpunished. John Land, the prosecutor who let him walk free, was the son of Aaron Land, who led the 1912 lynching of a black teenage boy.

John Land went on to become a judge and heard the pre-trial stages of the Stocking Strangler case – when he made rulings that denied Gary's defence a cent of public funding. Later, in 2007, his nephew Clay Land, also a judge, rejected one of Gary's previous appeals, though even then there was a mass of fresh evidence.

Superficially, race relations in Columbus have changed beyond recognition. Blacks and whites eat in the same restaurants and the city's schools have been desegregated – though this did not happen until the 1990s, 40 years after American educational apartheid was outlawed by the US Supreme Court.

But long-ingrained attitudes do not easily vanish and it is inescapable that while Gary is an African-American, all the strangler's victims, elderly women who lived alone, were white. Many of their relatives were present in court last week, sitting on the benches behind the four prosecution lawyers, led by the Columbus District Attorney Julia Slater. Among them were retired police officers and others who played prominent roles in the case, such as Ms Slater's predecessor, Bill Smith, who prosecuted Gary at his trial and went on to become chief judge for Columbus and the six surrounding counties.

One man, former Detective Michael Sellers, whose work was chiefly responsible for Gary becoming a suspect, could not contain himself. He spent much of the hearing staring at me and Gary with undisguised hatred, at one point meeting my eyes and mouthing: 'F*** you.'

At the end of the second day, he approached Jack Martin and me and asked how we could look at ourselves in the mirror. 'You'll soon be looking at yourselves in hell,' he said. He was led away by deputies, still berating us.

In fairness to Sellers, Martin was not sparing in his criticisms of him as he summarised the case in court. At a hearing in 2014, evidence was presented of the size 9½ shoe print left by the killer when he climbed into a victim's home – one of the many items concealed from Gary's original trial.

TV footage from day two of testimony in the Carlton Gary Stocking Strangler case

This was awkward for the prosecution because, as I confirmed in court by measuring Gary's feet with a shoe shop gauge, they are size 14.

Sellers also testified about the shoe print. For the first time in 30 years he made the extraordinary claim that when he arrested Gary he removed his shoes and saw that his toes were 'all bent up' because he habitually wore shoes that were far too small for him in order to confuse detectives.

Making his closing speech on Friday, Martin was withering. 'Gary could not have worn that shoe,' he said, adding that Sellers had merely demonstrated that he just 'made stuff up'.

Sellers was the only police witness to testify at the trial about Gary's supposed confession, a document written from 'memory' without any tape recording or contemporaneous notes. Martin said Sellers' lack of reliability meant the confession was worthless. Martin ended by asking the judge to imagine he was making a speech to a jury which had heard all the fresh evidence which has emerged since the 1986 trial. He summarised some of it.

There was the shoe print; the DNA test; a cast made from a savage bite wound left by the killer displaying dental deformities that Gary does not have; forensic analysis showing that the killer, unlike most of the population – including Gary – did not produce certain biological markers in his semen; and there was that police artist's sketch.

But his harshest comments came when he spoke of the astonishing act of sabotage by the Georgia state crime lab which destroyed the most critical evidence of all: a semen sample swabbed from the abdomen of victim Martha Thurmond soon after she was murdered.

Somehow, in breach of every scientific protocol, when this sample was sent for DNA testing in 2010 it was contaminated by a much larger sample of fresh semen produced by an unknown laboratory worker, 'swamping' the original sample from the victim and rendering it unusable – an event that has never been explained.

'They had in their hands life-or- death evidence, and a responsibility to do good, accurate testing,' Martin told the court. 'And what did they do? They destroyed it. That one fact must now take the death penalty off the table.'

He also reminded the court that the prosecution was claiming the same lab had found a match between Gary's DNA and a swab from another victim, Jean Dimenstein. Yet mysteriously, it had emerged that an envelope which should have contained a sample of semen from Gary and was then permanently sealed had been opened, and the sample was missing.

'Tell me that a jury wouldn't wonder if that swab had contaminated the Dimenstein test,' he said. 'That lab was not to be trusted.'

Responding to Martin, District Attorney Slater did not attempt to refute any of the fresh evidence, other than to claim that the DNA test on Ms Miller's nightdress might have been the result of consensual sex with someone else – a suggestion Martin treated with contempt. 'There's no evidence she had any sexual partners,' he said. 'Come on. There's a man's life at stake. Be serious.'

Otherwise, she devoted her entire speech to a legal argument, claiming that whatever its impact, the judge should simply not consider any of the new evidence, because the defence should have presented it at earlier appeals. Martin had not exercised 'due diligence', she claimed, despite the fact that the prosecution had not only hidden crucial items which had always been in its files, but even lied about them.

At one 1994 hearing, when the defence tried to obtain the semen swabs for DNA tests, it was told they had been destroyed because they were a 'bio-hazard'.

Prosecutors sometimes complain that defence lawyers try to get their clients off on a 'legal technicality'. Ms Slater was turning this on its head, in effect arguing that Gary should be put to death on a technicality, though the way she saw it, this would 'give the community justice'.

Now it is down to Judge Jordan. In the next few weeks he will decide whether to quash the convictions and order a retrial, to commute Gary's sentence or to send him to the death chamber.

He left the court with Martin's last words ringing in his ears: 'There is no way that a just society could execute this man.'