The Hammersmith Ghost murder case of 1804 set a legal precedent in the UK regarding self-defence: that someone could be held liable for their actions even if they were the consequence of a mistaken belief.
Near the end of 1803, many people claimed to have seen or 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 January 3, 1804, a 29-year-old excise officer named Francis Smith, a member of one of the armed patrols set up in the wake of the reports, shot and killed a bricklayer, Thomas Millwood, mistaking the white clothes of Millwood's trade for a shroud of a ghostly apparition. Smith was found guilty of murder and sentenced to death, later 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]
The Judge said it must be either murder, or of acquittal. If the jury believed the facts, there was no extenuation that could be admitted; for supposing that the unfortunate man was the individual really meant (ghost), and had been shot, the prisoner would have been guilty of murder.