Homicidal somnambulism or more commonly, homicidal sleepwalking is a formally recognised disorder. Quite interestingly it has been used as a working legal defence in around 68 cases, most recently in 2009.
One example of homicidal sleepwalking was by Albert Tirrell in 1846 for the murder of a prostitute. That prostitute was Maria Bickford, she and Albert had fallen in love and had begun living together. On October 27, 1845, Albert was accused of going up to Maria’s room after her final customer and, using a razor, cut her neck from ear to ear. He was also accused of setting off a series of fires within the brothel. However, there was no eyewitness to the event, and all evidence against Tirrell was circumstantial. His Lawyer used this to his advantage arguing that Tirrell had no motive to kill Bickford and that there could only be a few explanations for what had happened. Either, Bickford could’ve committed suicide, which was extremely implausible, or Tirrell, as a known sleepwalker, could have murdered Bickford under the influence of a dream. At the time very little was known about the causes of sleepwalking, which allowed for his lawyer to fantastical descriptions of sleepwalking that emphasised violence. After only two hours of deliberation, the jury deemed Tirrell not guilty, making it the first time sleepwalking was used as a working legal defence for murder in American legal history.