THE SCAPEGOAT of the Old Testament was a blameless goat sent into the wilderness to perish, symbolically bearing the sins of Israelites in a ritual form of guilt-purging: the “scape” in scapegoat derives from “escape”. Sometimes, we must assume, the poor creature did escape the fate intended for it, and found its way back to the herd. The rehabilitation of the innocent is one of the most profound acts any society can undertake, since it means acceptance of guilt, not avoidance of blame.

This week Jacques Chirac declared that Alfred Dreyfus, France’s most notorious victim of miscarried justice, was entirely innocent, 100 years to the day after he was finally acquitted of treason. In 1894 Captain Dreyfus, a young officer in the French Army, was accused of spying for Germany. He was stripped of his rank, subjected to intense psychological pressure in a failed attempt to extract a confession, found guilty anyway and sent to Devil’s Island off French Guiana, where he was afflicted by malaria, depression and dysentery. The only crime Dreyfus had committed was to be Jewish, when anti-Semitism and spy-fever had combined in a toxic brew; he was convicted on the ground of pure prejudice, backed up by the law.

Dreyfus was defended, most famously, by the novelist Émile Zola, and eventually pardoned, but his guilt and innocence have been argued over by Right and Left ever since. The homage paid to Dreyfus marks, in President Chirac’s words, a victory against “the dark forces of intolerance and hatred”.

The same apology should now be extended, in Britain, for Alan Turing. At first sight, there might seem to be little in common between the French officer and the oddball Cambridge mathematician who helped to win the Second World War by breaking Nazi codes, and thus created a blueprint for the modern computer. But both were patriots and heroes, and both were victimised, amid fear of foreign espionage, because they were different: Dreyfus for being Jewish, and Turing because he was homosexual.

Turing was found dead in his bed, in 1954, at the age of 41, after taking a bite from an apple laced with cyanide. Two years before he had been convicted of gross indecency for a homosexual affair, and forced to undergo oestrogen hormone injections, a primitive attempt to “cure” his sexual inclinations that caused him to grow breasts. His arrest and conviction led, in the words of David Leavitt, his latest biographer, to “a slow, sad decent into grief and madness”.

It was a most peculiar suicide, but then Turing was a man of many oddities, and a singular genius: he could limn the beauty of numbers. He became at the age of 22 a mathematics lecturer at King’s College, where homosexuality was unremarkable before the war. His fellow fellows made up a ditty: “Turing/Must have been alluring/To get made a don/So early on.”

In 1939 Turing was recruited to Bletchley Park, the Government’s code-breaking centre, to devote his mathematical skills to cracking Nazi encryption. With perseverance, inspiration and help from brains scarcely less brilliant than his own, Turing invented an electro-mechanical logic machine that could eliminate billions of possible solutions and gradually home in on the code. By 1941 the Enigma code had been broken, and the U-boat threat blunted, thanks, in large part, to this strange, unkempt, gay man who held his trousers up with string. Some 6,000 people knew that Enigma had been broken, and not one of them let the story leak: it was the best-kept secret in history.

Turing’s machine was called the Bombe, in part because of the way it ticked as it “thought” its way towards a solution. Very few understood how it worked; and even fewer understood what made Turing tick. He was an obsessive runner; he chained his mug to a radiator at Bletchley Park, fearing theft; like some other great thinkers he was almost certainly an undiagnosed autistic.

In 1952, when reporting a burglary to the police, he naively admitted to a relationship with a rent boy. Instead of a prison sentence, the judge ordered psychoanalysis and a year’s chemical treatment for a condition then regarded with horror as a combination of illness, mental frailty and immorality. It is hard to see Turing as anything other than a victim of homophobia, but like Dreyfus he was also prey to the political paranoia of the times.

The scandal of Burgess and Maclean had firmly equated homosexual “vice” with treachery. In the Cold War miasma of suspicion and intolerance, Turing’s homosexuality and his knowledge of British intelligence secrets made him a security risk: perhaps, to quote the title of Leavitt’s book, he “knew too much”.

Turing’s was a discreet martyrdom. The great and good did not come forward, as they had for Dreyfus, to defend a man being persecuted not for anything he had done, but for what he was. Turing’s wartime role was still unknown, for the truth about Bletchley Park and the Enigma code would not be revealed until the 1970s. His full contribution to computer science has become apparent only in the past two decades: every keyboard stroke you make, every tiny digital calculation of your PC, can be traced back to Turing’s machine. Yet even today he is less celebrated than he deserves, in part because of his sexuality, his conviction, his appalling treatment and his tragic end.

This week the French President praised Dreyfus as a great patriot, but in truth he was a brave and ordinary man wrenched from obscurity by bigotry. There was nothing ordinary about Turing, and his contribution to history was immeasurably greater. He was treated with a cruelty that today seems utterly abhorrent. A public acknowledgement of that would be a noble and timely gesture: then we could escape from the debate over his sexuality and get on with celebrating his extraordinary mind. Turing was not Dreyfus; all the same, j’accuse.

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