PORTLAND – A Waterville man burst into a Roman Catholic convent, stabbing and beating three elderly nuns and bludgeoning a fourth with a statue of the Virgin Mary. A Bangor woman systematically starved her 5-year-old daughter to death.

Both gruesome crimes were decided by a judge, not a jury. Both defendants were found not guilty by reason of insanity.

This week, a 32-year-old cook accused of killing and dismembering four people will go on trial using an insanity defense. But Christian Nielsen is seeking a trial by jury in Oxford County Superior Court in Paris.

Deciding who will determine guilt was one of the most important questions that faced Nielsen’s legal team. His lawyers concluded they were better off having jurors instead of a judge determine Nielsen’s fate.

“We feel that we can get 12 members in Oxford County who can fairly and impartially make a determination as to the issues regarding his mental health,” said Margot Joly, one of Nielsen’s defense lawyers.

Assistant Attorney General Andrew Benson declined comment, other than to say the defense decision was “unusual.”

A pool of more than 100 potential jurors has been set aside for the selection process, which is set to begin Wednesday.

But there are still questions of whether there will be a trial at all. Justice Robert Crowley will re-evaluate Nielsen’s competency the day before the trial begins because the 6-foot-tall Nielsen’s weight dropped by about 12 pounds, to 106 pounds, possibly impairing his cognitive ability. As of Friday, Nielsen weighed 114 pounds, Benson said.

Nielsen, 32, is charged with shooting and dismembering three women at the Black Bear Bed & Breakfast in the rural ski town of Newry. He’s also accused of killing a fourth victim, an Arkansas man who was partially dismembered and burned miles away at a remote, wooded location near Upton, authorities said.

Nielsen confessed to the crimes, so there’s little doubt who killed the victims. The question for jurors will be his mental status.

To win at trial, his lawyers must prove that he suffers from a “mental disease or defect” and that he did not appreciate the wrongfulness of his conduct, said Melvyn Zarr, professor at the University of Maine Law School.

Such cases often boil down to a “battle of the experts” and jurors are left to sort it out, but the burden of persuasion is on the defense, he said.

Defendants typically opt for a jury trial because all 12 jurors must agree to convict. All it takes is one holdout for a hung jury.

But defendants sometimes let a judge hear the evidence in a case like Nielsen’s if it’s particularly grisly, or if it’s a highly technical defense, said Laurie Levenson, a former federal prosecutor and Loyola Law School professor.

The defense team, however, could decide to put the case in a jury’s hands if pretrial rulings indicate the judge isn’t sympathetic, she said.

“It must be because their interactions with the judge so far indicate he’s not inclined to be sympathetic to the defense. So they’re playing the odds,” Levenson said. “To hang up that jury, they need only one.”

Perry O’Brian is one of the lawyers who represented Tonia Kigas, a Bangor woman who was accused of starving her 5-year-old daughter to death in 1993. The legal team opted to let a judge decide the case instead of a jury.

“It was just very emotional facts. It’s hard to have [jurors] separate their emotions and be objective,” he said. “With judges, you get the benefit of somebody looking coldly at the legal standard and seeing the evidence there to support it.”

The legal team came to the same conclusion in the case of Mark Bechard, who was found to be not guilty by reason of insanity for the attacks on the nuns, two of whom died.

Woody Hanstein, one of Bechard’s lawyers, said there was concern about the ghastly details of Bechard’s attack on the nuns in 1996 as well as concern that potential jurors might see an insanity defense as a ticket to freedom.

The reality is that killers who are found not guilty by reason of insanity are sent to secure facilities for treatment for years, he noted.

In Nielsen’s case, psychologists have testified that he suffers from schizoid personality disorder and possibly other mental health problems including Asperger’s syndrome, often described as a mild form of autism.

But unlike Kigas and Bechard, experts have testified there’s no evidence of full-blown psychosis for Nielsen. And unlike Bechard, who was hospitalized many times, Nielsen was sent to a psychiatric hospital only once, when he was a boy.