Why The Insanity Defense Is Rarely Effective

Two death penalty cases kicked off this week in King County Superior Court – both involve an insanity defense to some degree.

In one, Joseph McEnroe is charged with six counts of aggravated murder for teaming up with his girlfriend to kill her family, including two children, in 2007. McEnroe had asked to use the insanity defense, but a trial judge wouldn't allow it.

In the second trial, Christopher Monfort is saying he wasn't sane when he killed Seattle Police Officer Timothy Brenton in 2009.

The insanity defense is a bit of a Hail Mary for defense attorneys. Seattle University law professor Deborah Ahrens told KUOW’s Ross Reynolds that it’s uncommon for a defendant to be found not guilty by reason of insanity – fewer than 1 percent of felony cases.

“It happens a lot more on TV or in movies,” she said.

Ahrens, a former public defender, said defendants who plead not guilty by reason of insanity typically have an underlying mental illness – and an expert witness who will testify that they weren’t sane when they committed the crimes.

“They didn't know the difference between right and wrong, or they didn't understand sort of the nature of their act in the first place,” she said.

About 22 people each year are found not guilty by reason of insanity in Washington state, according to a report in the Journal of the American Academy of Psychiatric Law. Of the total number institutionalized, about 27 percent committed homicides.

It’s a tougher defense to mount for murder cases. That’s because jurors on death penalty cases are generally tougher on crime – for starters, they must be willing to apply the death penalty.

“There are studies that demonstrate that people who are willing to apply the death penalty are perhaps somewhat more likely to convict,” Ahrens said.

Governor Jay Inslee has said Washington state won’t execute death row inmates while he’s in office. But that doesn’t prevent prosecutors from pursuing the death penalty for McEnroe and Monfort. Given the long appeals process in death cases, chances are good that their clemency appeals could end up on another governor’s desk.

If Monfort’s defense does succeed, he wouldn’t get to walk free. He would be committed to a secure mental institution, which could turn into a life sentence.

“Someone who is that mentally ill is going to take quite some time to be treated,” Ahrens said.

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