Do ghosts legally exist? The 1991 Supreme Court of New York State case Stambovsky v. Ackley was a court case over the existence of ghosts, and it concluded that for legal purposes, they can.
The actual matter and legal decisions found in Stambovsky v. Ackley were a bit more dry, as legal matters tend to be. Helen Ackley had owned a house in Nyack, New York for over a decade, and had widely publicized that the house was haunted, including in articles in Reader's Digest. She sold the house to Jeffrey Stambovsky, without informing him of the house's history or her personal experiences with it, and her personal belief that it was haunted. When Stambovsky found out about the house's history, he sued to get the contract rescinded. The case ended up in the New York State Supreme Court (which is not actually the highest court in New York, but that is an unrelated issue). The five-judge panel voted, 3-2, in favor of the plaintiff, and rescinded the contract of sale. The judges didn't comment directly on whether ghosts existed, but did consider whether the defendant believed that they did, and that the property value could be effected, "Whether the source of the spectral apparitions seen by defendant seller are parapsychic or psychogenic".
The legal ruling rested on two poles, and had more to do with the legal doctrine of caveat emptor then parapsychology. They said that while in normal purchasing, it is a buyer's responsibility to inspect for defects, the haunting is not something that "the most prudent purchaser" could detect. The legal finding has more to with the level of responsibility and ability that a purchaser needs to bring to a transaction than with the existence of the supernatural. The ruling also touches on a seller's responsibility in reporting. While a seller does not have to report everything, if they have made something widely and publicly known, they are then required to inform people with a particular interest. The court said that if the seller felt the need to inform the public at large about the paranormal presence on the property, it then stands to reason that she should have informed someone who would be directly concerned. For these two reasons, the court found in favor of the plaintiff.
While the legal reasoning of the case was rather technical, the judges had a bit fun, sprinkling references to ghosts and the supernatural into the text, and referencing Hamlet and Ghostbusters. The judgment itself is rather short and entertaining, and clear to the layperson:
I have found no mention whether the precedent in Stambovsky v. Ackley has been applied to other areas of law, especially criminal law. Since Stambovsky seems to argue that it is intent and belief that is important, not the factual existence of the supernatural, it could be argued that in a criminal context, someone who used supernatural means to harm another person would be legally responsible. If someone was to point a magic wand at another person, believing that they could magically kill them with it, would they be be legally guilty of attempted murder? This ruling seems to suggest that it is so. However, this has never came up in a trial, as far as I know, probably because in such a situation, other matters (such as the competency of the defendant) would probably take up more time. However, according to Stambovsky v. Ackley, ghosts and the supernatural, or at least the belief in them, are legally valid.