LEWISTON – The man accused of murdering three women and a man over Labor Day last year is expected to claim he was not criminally responsible for his actions because he was mentally ill at the time.

How likely Christian Nielsen is to succeed with that defense will depend on conclusions drawn by his and the state’s psychologists, who have investigated his mental state during the slayings.

While the public may view an insanity plea as an attempt to skirt justice, experts say the opposite is true.

An insanity plea is rarely used in Maine because state law requires defendants to provide a preponderance of evidence that they were not criminally responsible.

If Nielsen succeeds in his effort, he would be committed to the state’s psychiatric hospital in Augusta for an indefinite period. He might never leave.

Dating back to 1970, nearly 60 people who invoked the insanity defense are in state custody, 22 of them at Riverview Psychiatric Center in Augusta. The others are living in halfway houses or supervised apartments. A few are serving prison sentences. All but possibly one suffer from mental illness, says State Forensic Service Director Ann Leblanc, a clinical psychologist who oversees the state’s mental health evaluations. That one person probably suffered from a personality disorder, she said.

Once committed, the former defendants can’t leave state custody until they prove to a judge they no longer pose a threat to themselves or others.

Three were released last year from the custody of the commissioner at the Department of Health and Human Services; three were newly committed.

Rare in Maine

In Maine, the so-called insanity defense is rarely used. Leblanc says a “small percentage” of defendants evaluated by the state’s psychologists actually proceed to trial asserting they are not criminally responsible because, as a result or mental disease or defect, they lacked substantial capacity to appreciate the wrongfulness of their criminal conduct. That wording is taken from state law.

Only a handful, up to a half-dozen, succeed each year, she said.

She doesn’t track the number of cases that go to trial. National statistics are outdated and wouldn’t necessarily be accurate because other states have different insanity laws, she said. Maine’s has changed substantially over the years. Four states allow no insanity defense.

In nearly all insanity cases in Maine, the defendants were charged with serious felonies, such as homicide, kidnapping or arson, and were facing long prison sentences if convicted. Otherwise, the unknown length of stay they face if committed to Riverview is not an attractive alternative.

According to statute, only those who suffer “severely abnormal mental conditions that grossly and demonstrably impair a person’s perception or understanding of reality” are eligible for an insanity defense.

Many have tried to fake it, but it’s not easy to feign severe mental illness for more than a couple of days or even hours, Leblanc said.

“Most people can’t do it long enough to be convincing,” she said.

Those who try to deceive experts likely suffer from mental illness but attempt a more severe form or a different diagnosis from their own, she said.

‘Very difficult’ burden

And just because somebody is diagnosed with mental illness doesn’t necessarily mean that person lacked the substantial capacity to appreciate the wrongfulness of their actions, said Charles Robinson, a consulting psychologist from Manchester who has testified in about a dozen insanity cases over two decades.

Not every evaluation results in a court appearance, he said. In fact, most don’t.

“In the last three or four cases, I told the lawyers, ‘OK, here’s what I think.’ There was no trial,” he said.

If his conclusions match those of the state’s experts, an agreement for commitment might result or the defense might not seek an insanity defense at all. That is happening more as the science of mental illness progresses, leaving less room for conflicting conclusions, he said.

Most defendants found not criminally responsible in the cases in which Robinson has been involved suffer from schizophrenia or bipolar disorder, he said.

Proving a defendant is not criminally responsible is a hard tack to take in court, the Manchester psychologist said.

“It’s a very, very difficult burden to meet,” he said.

At most criminal trials, the burden is on the state to prove guilt beyond a reasonable doubt. The insanity plea is called an affirmative defense because the defendant bears the burden of proving by a preponderance of evidence that he or she is not criminally responsible.

Robinson said he simply shares his findings and facts with the court when he takes the stand and doesn’t try to persuade anyone to see things his way. Judges and juries would be able to see through that.

“It’s not possible to be slick or to fool people,” he said.

Melvyn Zarr, a law professor at Maine Law School in Portland, said the outcome of insanity cases hangs on the testimony provided by psychologists.

“Usually, the result is dictated by what the experts say,” he said.

A sharp prosecutor will try to exclude the defense evidence supporting an insanity plea and ask the judge not to give the jury the option of finding the defendant not criminally responsible due to a lack of evidence.

Nielsen had no history

Nielsen’s attorney has said his 32-year-old client had no history of violent behavior before the slayings. Since he has been in custody, however, he reportedly has attacked another jail inmate and slashed his own forehead with a razor.

Robinson said a person’s history of mental illness and past actions are not always predictors of future behavior.

Some people are able to control their mental illness. Sometimes an illness progresses to a point where the person experiences a break and snaps into violent behavior.

In determining whether a person was not criminally responsible at the time of his or her actions, Robinson said he conducts an investigation that goes far beyond an interview with the defendant, which usually ranks near the bottom of his evaluation.

That investigation will include interviews with other people familiar with the defendant, medical and other personal records and videotapes of police interviews with the suspect. All elements are assigned different levels of importance, he said.

Most people who end up pleading not criminally responsible are quickly caught by police, Robinson said.

That was the case with Nielsen, who confessed to killing the four victims, according to a Maine State Police affidavit.

He said he shot James Whitehurst, 50, of Arkansas, in the back of the head on their way to Upton for some fishing. He started to dig a grave to bury Whitehurst’s body, then attempted to burn it. He never told police why he killed Whitehurst.

At the Black Bear Bed and Breakfast in Newry, where he lived, Nielsen decided to shoot the inn’s owner, Julie Bullard, 65, in the chest three times because she might suspect him of being responsible for Whitehurst’s disappearance, he reportedly told police.

He shot Bullard’s daughter, Selby Bullard, 30, and her friend, Cindy Beatson, 43, in the head after they surprised him at the bed and breakfast, according to police reports.

He took the bodies outside and dismembered them with a chain saw and a hacksaw, police said.