Thrice married 40-year-old former nurse who is regarded as Britain’s greatest mass murderer.

Mary Cotton went to West Auckland in County Durham in 1871 with her bigamous husband, Frederick, his two stepsons and her own 6-month-old baby. Within two months Frederick died at the age of 39 of gastric fever, and a short while later one of Mary’s lovers, Joseph Natrass, moved in as a lodger.

Meanwhile Mary had become pregnant by a local excise officer called Quick-Manning. Between 10 March and 1 April 1872 there were three more deaths in Mary’s house - Natrass , her own baby and her late husband’s elder boy, aged 10.

On 12 July the other cotton stepson died, and a suspicious neighbour went to the police.

The doctor, who had seen the child the previous day, refused to give a death certificate. A postmortem was carried out, and analysis of the stomach contents proved positive for arsenic. Exhumations of two of the other deaths in the Cotton home also showed that arsenic was responsible.

Mary Cotton was charged with murder of her stepson and taken to Durham Prison, where her child by Quick-Manning was born. She pleaded not guilty at her trial at Durham Assizes in March 1873. The defence line was that the dead boy had been poisoned accidentally by arsenic contained in green floral wallpaper used in his home. But Mary’s purchase of soft soap and arsenic (ostensibly for cleaning bedsteads and destroying bedbugs) proved ominous. She was found guilty, and sentenced to death.

The home secretary refused to commute the sentence, despite a mounting wave of sympathy. Mary’s baby was taken from her five days before she was hanged in Durham prison on 24 March 1873. The hangman did his work badly, and it was three minutes before the body stopped convulsing at the rope's end.

Mary Ann Cotton, whose life consisted of a trail of deaths - twenty-one persons close to her died within twenty years - was suspected of 14 or 15 murders. Her motive was either to gain insurance money or to pave way for a new marriage.