The definitions of legal insanity differ from state to state, but generally a person is considered insane and is not responsible for criminal conduct if, at the time of the offense, as a result of a severe mental disease or defect, they were unable to appreciate the nature and quality or the wrongfulness of their acts.
The standard for claiming a defendant as being not guilty by reason of insanity has changed through the years from strict guidelines to a more lenient interpretation, and then back to where it is today, a more stringent standard.
Listed below are some of the high-profile cases when defendants used legal insanity as their defense. In some cases, the juries agreed, but more often than not, the criminals were found sane enough to know that what they were doing was wrong.01of 06
John Evander Couey
In August 2007, John Evander Couey, the man convicted of kidnapping, raping and burying nine-year-old Jessica Lunsford alive, was declared sane enough to be executed. Couey's attorneys argued that he suffered lifelong mental abuse and had an IQ below 70. The judge in the case ruled that the most credible exam rated Couey's IQ at 78, above the level considered mentally disabled in Florida.
Couey, however, bypassed being strapped to a gurney. Instead, he died in a prison hospital on August 30, 2009, from natural causes as a result of having cancer.02of 06
At one time Andrea Yates was a high school valedictorian, champion swimmer, and college-educated registered nurse. Then in 2002, she was convicted of capital murder for killing three of her five children. She systematically drowned her five children in the bathtub after her husband left for work.
In 2005, her conviction was overturned, and a new trial was ordered. Yates was retried in 2006 and found not guilty of murder by reason of insanity.
Yates had a long medical history of suffering from severe postpartum depression and postpartum psychosis. After giving birth to each of her children, she displayed extreme psychotic behavior that included hallucinations, attempted suicides, self-mutilation, and an irresistible impulse to hurt the children. She had been in and out of mental institutions over the years.
Just weeks before the murders, Yates was released from a mental hospital because her insurance stopped paying. She was told by her psychiatrist to think happy thoughts. Despite warnings from her doctors, she was left alone with the children. This was one of the cases when the plea, innocent by reason of insanity, was justified.03of 06
Mary Winkler, 32, was charged with the first-degree murder on March 22, 2006, for the shotgun shooting death of her husband, Matthew Winkler.
Winkler had been serving as the pulpit minister at the Fourth Street Church of Christ in Selmer, Tennessee. He was found dead in his home by church members after he failed to show up for an evening church service that he was scheduled to lead. He had been shot in the back.
A jury convicted Mary Winkler of voluntary manslaughter after hearing testimony that she was physically and mentally abused by her husband. She was sentenced to 210 days and was free after 67 days, most of which was served in a mental facility.04of 06
Anthony Sowell is a registered sex offender who is accused of killing 11 women and keeping their decomposing bodies in his home. In December 2009, Sowell pleaded not guilty to all 85 counts in his indictment. The charges against Sowell, 56, ranged from murder, rape, assault and corpse abuse. However, Cuyahoga County Prosecutor Richard Bombik said there was no evidence that Sowell is insane.05of 06
Lisa Montgomery tried to use mental illness when she was being tried for strangling eight-month pregnant Bobbie Jo Stinnett to death and cutting the unborn child from her womb.
Her lawyers said she was suffering from pseudocyesis, which causes a woman to falsely believe she is pregnant and exhibit outward signs of pregnancy. But the jury didn't buy it after seeing evidence of the methodical plan Montgomery used to lure Stinnett into her deadly trap. Montgomery was found guilty and sentenced to death.06of 06
Ted Bundy was attractive, smart, and had a future in politics. He was also one of the most prolific serial killers in U.S. history. When he was being tried for the murder of one of his many victims, Kimberly Leach, he and his attorneys decided on an insanity plea, the only defense possible with the amount of evidence the state had against him. It did not work, and on January 24, 1989, Bundy was electrocuted by the state of Florida.