Alias Grace was inspired by a real-life Canadian murder case. Thomas Kinnear and his housekeeper, Nancy Montgomery, were killed on 23 July 1843. Kinnear was shot, Nancy was strangled, and both bodies were dumped in Kinnear's cellar. Nancy was Thomas Kinnear's mistress, and at the autopsy, she was found to be pregnant.
Immediately after the murders, Kinnear's sixteen-year-old maid, Grace Marks, and his manservant, James McDermott, escaped to the USA. When they were caught and arrested, they were wearing their victim's clothes and carrying their possessions.
The Kinnear-Montgomery murders became a sensation in nineteenth-century Canada. Newspaper reports of the trial emphasized the gory nature of the crime and the shocking fact that a "gentleman" had been murdered by his servants. Reporters also took a great deal of interest in the sexual aspects of the story (Nancy's pregnancy and the alleged relationship between James McDermott and Grace Marks.)
During the trial, McDermott admitted to shooting Thomas Kinnear and to killing Nancy. However, the extent of Grace's involvement in the murders was unclear. McDermott claimed that Grace was jealous of Nancy and talked him into the murder. He also claimed that Grace helped to strangle Nancy when a blow to the head failed to kill her. Grace told several different stories before, during and after her trial. Sometimes she claimed that she was not present when the murders took place. At other times, she admitted to being involved but said that McDermott had intimidated her into committing the crime.
McDermott and Grace were both found guilty: McDermott for the murder of Thomas Kinnear and Grace as an accessory to his murder. James McDermott was hanged shortly after the trial. Grace's death sentence was reduced to life imprisonment thanks to the appeals of her lawyer and a group of petitioners.
Grace began her sentence at Kingston Penitentiary on 19 November 1843. Roughly nine years later, she transferred to Toronto Lunatic Asylum for a short time. This was because she was allegedly suffering from hallucinations, insomnia and mood swings. After serving almost thirty years in prison, Grace Marks was granted a Pardon. She became a free woman in 1873 and moved to New York.