On May 15, 1886, John Law, who kept a café in Ashton-under-Lyne, called at the Dixon house on Turner Lane to arrange the catering for Mary Dixon's funeral. She had died the day before, at twenty-nine. The woman who let him in was a neighbor who had been staying there, Mary Ann Britland, and she startled him with questions about poison. She told him she had bought some rodent killer. He asked whether she had told Thomas Dixon, the widower, and she had not; when Dixon came home she told him, and Law, who later gave evidence, said Dixon was horrified. That afternoon a post-mortem was carried out in the house and organs were sent away for analysis. Someone had already written anonymously to the police.
Britland was born Mary Ann Hague in Bolton in 1847, the second eldest daughter of Joseph and Hannah Hague, and married Thomas Britland at St. Michael's Church in Ashton-under-Lyne in 1866. They rented 133 Turner Lane with their two daughters, Elizabeth Hannah and Susannah. She worked two jobs, as a reeler in a local mill by day and as a barmaid at night. The Dixons lived across the street at number 128. Thomas Dixon, a twiner, was several years younger than his wife, and he and Mary Ann Britland had begun an affair.
In February 1886 she went to a chemist's near her home, said she had mice, and bought several packets of Harrison's Vermin Killer. Because it contained strychnine and arsenic she had to sign the poison register. On March 8 her daughter Elizabeth, nineteen, fell ill with convulsions and vomiting, and her mother nursed her until she died two days later. The doctor certified convulsions and spasms of the heart. The woman who laid out the body noticed that Elizabeth's hands were tightly clenched. Britland collected £10 on her life. On April 30 her husband, Thomas, forty-four, became violently ill after a meal with her; he died on May 3, and the death was put down to epilepsy. She collected £20. The Dixons, shocked by their neighbor's double loss, took her in. Eleven days later Mary Dixon was dead, with the same clenched hands.
The analysis found arsenic and strychnine in Mary Dixon's stomach and tissues, and Britland and Thomas Dixon were both arrested. At Ashton police station she confessed that she had wanted to marry Dixon, that she had poisoned Elizabeth first because she believed her daughter suspected what she intended, and then her husband, and then Mary Dixon. Dixon was quickly shown to have had no part in it. The chief constable, Dalgleish, told the magistrates that strychnine had caused Mary Dixon's death, and they remanded Britland and refused her bail. By order of the Home Secretary, Elizabeth and Thomas Britland were exhumed, and on June 16 the court heard that their stomach contents had gone to the analyst.
She was tried at the Manchester Assizes before Mr. Justice Cave on July 22, 1886, with Mr. Addison prosecuting and Mr. Blair defending. She was tried only for Mary Dixon's murder, but the other two deaths were put in evidence to show system and rebut any defense of accident, and Dr. Harris told the court of the poison he had found in the exhumed bodies. Her defense argued that the few pounds of insurance could never have been worth a husband and a daughter. An observer at the trial wrote that she had bought enough "mouse powder" to kill all three with no sign of any mice to use it on, and that she had talked indiscreetly about poison and had been anxious to learn whether it could be traced after death. The jury took some time but convicted her. After sentence she told the court: "I am quite innocent; I am not guilty at all."
On the morning of August 9, 1886, she was in a state of collapse. Two female warders half carried her from the condemned cell as she wailed and begged for mercy, and held her on the trapdoors while James Berry prepared her; then two male warders took their place. Her last words were "Oh Lord save me! Have mercy upon me." Berry gave her a drop of seven feet. She was the first woman hanged at Strangeways and the second woman Berry had executed. Only three more women were ever hanged there: Louie Calvert, Margaret Allen and Louisa May Merrifield.