The conviction of the guilty is just; it is the unremarkable business of a just criminal jurisprudence; but the conviction of the innocent strikes at the heart of justice. If it happens through error or negligence, it is bad enough; when it happens by design, it is an abomination that corrodes trust in the law itself.
Maimonides in the 12th century, in this commentary on Exodus 23:7 (Keep far from a false charge, and do not kill the innocent and righteous, for I will not acquit the wicked) concluded, “it is better and more satisfactory to acquit a thousand guilty persons than to put a single innocent man to death once in a way.”
Practical men, especially those who reasonably expect never to suffer the consequences of flawed jurisprudence, have taken a more pragmatic view than Maimonides. So English Chief Justice John Fortesque, in 1471, revised the number drastically. “Indeed I would rather wish twenty evil doers to escape death through pity, than one man to be unjustly condemned.” Later still, Lord Blackstone in the late 1760s widened the scope to all crime and punishment, writing, “Better that ten guilty persons escape than that one innocent suffer.” This last has become a fundamental maxim of common law criminal justice, generally known as Blackstone’s Ratio.
Statesmen, and the secret police, can have their own sense of the practical. Otto van Bismarck supposedly remarked that “it is better that ten innocent men suffer than one guilty man escape.” Felix Dzerzhinsky, founder of the Cheka, perpetrator of the Red Terror, head of the OGPU/NKVD, was more to the point. “Better to execute ten innocent men than to leave one guilty man alive.” One of his successors, Nikolay Yezhov, restated his argument. “Better that ten innocent people should suffer than one spy get away.” What he meant by “suffer” was illustrated, as in the pictures below, when he fell foul of the Great Purge which he had orchestrated: he was executed in 1940.