If you watch the film "10 Rillington Place" your heart will break. The illiterate simpleton Timothy Evans was hanged in 1950 for the murder of his baby daughter. His wife's body had been found with the little girl's, but he was not charged with her murder.
Evans and his wife were lodgers in the house of John Reginald Christie.
Three years later Christie was hanged for the murders of several women whose bodies were found in the house after he moved out. One of them was his own wife.
Even though he confessed to killing Beryl Evans, Timothy's wife, the authorities found it easier to believe there were two multiple murderers operating separately in one house at the same time, than that they had made a mistake and Evans was innocent. He had confessed, after all, but he was easily manipulated by Christie and by the police. Christie made him believe that he would be held equally liable for the death, having persuaded him that she died as a result of an abortion Evans had agreed Christie could perform. (In fact she had been strangled.) The police took advantage of his suggestibility and weak-mindedness to get him to sign a series of confessions. But Evans had given himself up, thus opening up the original investigation that resulted in his execution.

Timothy Evans
John Hurt as Timothy Evans in the film. Quite an amazing resemblance.
John Reginald Christie
Richard Attenborough as Christie. Doesn't he do a great line in slimey villains?
It took the powers that be years to pardon Evans for the murder of his daughter, but they maintained that he had actually killed his wife, even though he had not been charged with it, and had therefore been legitimately executed. He was not granted a full pardon till 1966. The case is extrememly involved, and I may not have done justice to the facts. But after reading about it or seeing the film, no-one could ever support the death penalty again. What use is a pardon to a dead person?
There's quite a detailed account at this address: http://www.parmaq.com/truecrime/Rillington.htm
"10 Rillington Place" is showing in TCM in the UK at various times over the next week or two.
Rillington Place was later demolished and the new development renamed, probably Bartle Road, and is tucked alongside the A40(M) in west London.