In films, a detective hypnotizes a witness, who suddenly recalls the getaway car’s number plate in perfect detail. For a while, real police forces hoped it worked like that. The story of why they largely stopped is a lesson in how memory really works.
The case that started it
In July 1976, in Chowchilla, California, three armed men hijacked a school bus carrying 26 children and their driver. They drove their captives to a quarry and shut them in a truck trailer buried underground. After about sixteen hours, the driver and the older children dug their way out.
Neither the driver nor the children could give useful details about the kidnappers. Under hypnosis, the driver recalled all but one digit of the number plate on one of the vans. That lead helped investigators identify the three men, who were convicted.
The case was a sensation, and “investigative hypnosis” spread quickly through American police forces.
What the science found
When psychologists tested hypnotically refreshed memory under controlled conditions, the results were troubling.
- People report more. Hypnosis increases the amount recalled.
- More of it is wrong. The extra material includes errors and inventions as well as accurate details.
- Confidence goes up. People become more certain of what they recall, whether it is right or wrong.
- They are more suggestible. Leading questions have more effect.
- Source is lost. Afterwards, people cannot tell which memories they had before hypnosis and which arose during it.
The confidence effect is especially damaging in court. Juries find confident witnesses persuasive, and cross-examination does little to shake a witness who sincerely believes a false memory.
Chowchilla was a genuine success, but a number plate can be checked. Most recalled details cannot.
How the courts responded
American courts took different routes.
Safeguards. In State v. Hurd (1981), the New Jersey Supreme Court allowed hypnotically refreshed testimony only if strict conditions were met: a qualified, independent professional, a record of what the witness remembered beforehand, and a recording of every session. In that case, an officer had asked the hypnotized victim whether her attacker was a named man, a clear example of a leading question. New Jersey later abandoned this approach and excluded such testimony.
Exclusion. Many states adopted a rule that a witness who has been hypnotized cannot testify about what they recalled afterwards.
The defendant’s exception. In Rock v. Arkansas (1987), the US Supreme Court ruled by five votes to four that a state cannot use a blanket ban to stop a defendant giving their own hypnotically refreshed testimony, because defendants have a constitutional right to testify in their own defence.
Texas. Texas kept a police hypnosis programme longer than most. A newspaper investigation found the practice had been used close to 1,800 times over about forty years and had featured in cases that ended in death sentences. In 2023 Texas passed a law, in force from 1 September that year, barring statements obtained through investigative hypnosis from criminal trials.
Elsewhere
In the United Kingdom, official guidance has long discouraged police use of hypnosis, and a witness who has been hypnotized may not be called to give evidence.
Is there any role left?
Some argue hypnosis may still help generate leads that can be independently checked, as in Chowchilla, provided nothing recalled is used as evidence. Others say that even this risks contaminating a witness.
Police now more often use the cognitive interview, a structured technique based on memory research. It encourages a witness to recreate the context and report everything without guessing, and it improves recall with far less risk.
What this means outside the courtroom
The same findings apply to therapy.
- A memory that emerges in hypnosis is not thereby true.
- Vividness and confidence are not evidence of accuracy.
- A therapist should never use hypnosis to find out “what really happened.”
If you are a witness in, or party to, any legal matter, speak to a lawyer before having hypnosis. It could affect whether you are allowed to give evidence.
The bottom line
Hypnosis is a poor tool for finding facts. The courts learned that at real cost, and it remains one of the most important things to understand about hypnosis.
Next in the series: Hypnosis for Depression: An Emerging Option
This article is for general information and is not legal or medical advice.