7 Serial Killers Who Pleaded Insanity

Although pop culture often depicts the insanity plea as a common occurrence in the legal realm, it’s actually one of the rarest methods of defense. In order to prove an insanity plea, the defense must show that the killer did not realize what he or she was doing and also that they didn’t know the difference between right and wrong. Very few insanity pleas have worked in murder defenses and even fewer in the case of serial killers. Most serial killers who have pleaded insanity are unsuccessful in convincing a jury and are convicted regardless of their plea. 

When there is mounting evidence against a serial killer, sometimes the insanity defense is the best way to try to stay off death row. This defense, however, ensures that the criminal must admit that they committed a crime, so a later not-guilty plea is difficult or impossible. Even in cases where a killer has been found not guilty by reason of insanity, serving time in a mental hospital is required. In some cases, like with Albert Fish, the jury may acknowledge the killer is insane, but find them guilty anyway.

Which serial killers have pleaded insanity? The serial killers on this list used insanity pleas to defend themselves in court.


  • Anthony Sowell

    Anthony Sowell
    Photo: Cuyahoga County Police Department / Wikimedia Commons / Fair Use

    When Anthony Sowell, known as the "Cleveland Strangler," was on trial for killing 11 women, he pleaded insanity.

    Ultimately, Sowell, who buried the bodies around his Cleveland home, couldn't prove that he didn't know the difference between right and wrong and was sentenced to death.

    • Age: 63
    • Birthplace: East Cleveland, Ohio
  • Andrea Yates
    Video: YouTube

    Andrea Yates drowned her five children in the bathtub. She was convicted in 2002 and sentenced to life in prison. However, in a 2006 retrial, she pleaded not guilty by reason of insanity due to suffering from extreme postpartum depression. Her original sentence was reversed and she was acquitted of capital murder.

    Under the jurisdiction of the court for the duration of her original sentence, Yates will remain in a state mental hospital for the rest of her life unless she opts for a review in an attempt to be released.

    • Age: 58
    • Birthplace: Houston, Texas
  • Jeffrey Dahmer
    Video: YouTube

    Jeffrey Dahmer murdered, dismembered, raped, and cannibalized 17 men between 1978-1991.

    He pleaded not guilty by reason of insanity; however, the jury found him guilty on all counts. Sentenced to 16 consecutive life terms in prison, he was killed by another inmate in 1994.  

    • Age: Dec. at 34 (1960-1994)
    • Birthplace: West Allis, Wisconsin, United States of America
  • Kenneth Bianchi
    Photo: Los Angeles Sheriff's Department / Wikimedia Commons / Public Domain

    Kenneth Bianchi was one of the Hillside Stranglers who, in conjunction with his cousin, killed and raped at least 15 women in 1977 and 1978. Bianchi originally tried to claim that he suffered from multiple personality disorder, but was caught in his lies when psychiatrist Martin Orne met with him.

    He ended up pleading guilty and received six life sentences. 

    • Age: 71
    • Birthplace: Rochester, New York, USA
  • Albert Fish
    Photo: Unknown / Wikimedia Commons / Public Domain

    Albert Fish, also known as "The Boogeyman," "The Brooklyn Vampire," and several other names, bragged that he had "had a child in every state." It's uncertain how many victims he killed, but he was accused of murdering three children. Fish claimed that voices inside his head told him to kill children and, thus, pleaded not guilty by reason of insanity during his trial.

    The jury believed that Fish was insane, but wanted him executed anyway, so they found him guilty. He was sentenced to death and executed in 1936.

    • Age: Dec. at 65 (1870-1936)
    • Birthplace: Washington, D.C.
  • Ed Gein
    Photo: Bryanwake / Wikimedia Commons / Public Domain

    Ed Gein is best known as the inspiration for the Texas Chainsaw Massacre's Leatherface and Norman Bates. He was caught for killing at least two people, but was suspected of killing more due to the extensive human remains found in his home in the form of furniture, masks, belts, suits, and window shades.

    In his 1958 trial, his defense pled not guilty by reason of insanity and he was found unfit for trial. He was committed to a mental institution until 1968, at which time he was deemed fit for trial. Found guilty of one murder and ruled insane at the time of the murder, he was sent back to a mental facility where he died in 1984.

    • Age: Dec. at 77 (1906-1984)
    • Birthplace: Wisconsin, United States of America