Three officers were shot dead and two others crippled for life by a gang of eastern European anarchists during a bungled burglary in Houndsditch in the City of London in December 1910. The murders led two and a half weeks later to the famous Siege of Sidney Street, in which two of the suspects were killed and a firefighter suffered fatal injuries.
One of the gang, a Latvian Bolshevik called Jacob Peters, escaped hanging in London for the crimes and in 1917 returned to Russia, where he became deputy head of the Cheka secret police and was described as the "Robespierre of the Russian Revolution" before apparently falling victim to Stalin's purges.
Donald Rumbelow, a former City of London Police officer and author of The Houndsditch Murders and The Siege Of Sidney Street, said the memorial to the three murdered policemen was "long overdue". He said: "Until 1966, when you had the shooting of three policemen in Shepherd's Bush, it was the worst crime in British police history.
"Then there is the supreme irony that the actual killer gets away with it and goes on to be such a prominent figure in the Russian Revolution."