The Hammersmith Ghost murder case of 1804 set a legal precedent in the UK regarding self-defence: whether someone could be held liable for their actions even if they were the consequence of a mistaken belief.
Near the end of 1803, a number of people claimed to have seen and even been attacked by a ghost in the Hammersmith area of London, a ghost believed by locals to be the spirit of a suicide victim. On 3 January 1804, a member of one of the armed patrols set up in the wake of the reports shot and killed a plasterer, Thomas Millwood, mistaking the white clothes of Millwood’s trade for a ghostly apparition. The culprit, a 29-year-old excise officer named Francis Smith, was found guilty of murder and sentenced to death, commuted to one year’s hard labour.
The issues surrounding the case were not settled for 180 years, until a Court of Appeal decision in 1984.[2][3][4]