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Accused killer Dakota Theriot arrives to the Ascension Parish Courthouse Annex escorted by Ascension Parish Sheriff's Office Detective LaTonya Prejean, Friday, Feb. 1, 2019, in Gonzales, La.

On its face, the man who authorities say admitted to killing five people, including his own parents, in a two-parish shooting rampage last month would be a clear candidate for the death penalty.

But the top prosecutor in Ascension Parish has not come to a decision on the matter. And the district attorney in Livingston Parish said he is giving it a hard look, citing in particular reports that Dakota Theriot has struggled with mental illness.

"I think it's just prudent to get as much information as we can, especially in light of the reports that he might have had a mental health issue," District Attorney Scott Perrilloux said.

Perrilloux is taking the case to a Livingston Parish grand jury Thursday morning, seeking formal charges against Dakota Theriot on three counts of first-degree murder in the deaths of his girlfriend, Summer Ernest; her brother, Tanner Ernest; and her father, Billy Ernest.

First-degree murder opens up the possibility of the death penalty. But a mitigating issue like mental illness is just one of a number of factors, from the opinion of the victims’ families to the cost of a years-long appeal process.

Authorities have said Theriot was staying with the Ernests in a trailer outsider Walker when on the morning of Jan. 26 he took a handgun stolen from his father and shot three residents inside, killing each with a single bullet to the head. Shortly thereafter, authorities said, he jumped in Billy Ernest’s car and drove down to Ascension Parish, where he killed his parents in the same fashion before fleeing to Virginia.

Theriot confessed to killing all five people but did not offer a motive, law enforcement authorities have said.

In the years before the shooting rampage, Theriot had had repeated run-ins with the police and involuntary mental health holds, law enforcement records show. He threatened to burn down the family house with his parents inside, hallucinated and beat his ex-wife, who told Kenner Police that Theriot was schizophrenic.

Ascension Parish Ricky Babin has not presented his case to a grand jury in that parish, said office spokesman Tyler Cavalier.

Should grand juries in either Ascension or Livingston return an indictment for first-degree murder, the prosecutors could seek the death penalty. But if they did so, they would be bucking a national trend away from the punishment. The number of death sentences given each year across the U.S. has fallen from a high of 315 in 1996 to 42 in 2018, according to the Death Penalty Information Center, a nonprofit that studies the issue.

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Perrilloux, who has prosecuted dozens of murder cases in his 22 years as district attorney in Livingston, Tangipahoa and St. Helena parishes, said his first consideration is whether a jury would even agree to the death penalty.

In order to seek it, the prosecutor must first secure a unanimous jury verdict on the suspect’s guilt and then a second, also unanimous verdict on a death sentence. Mental health is one of a multitude of issues that defense attorneys can bring up as they try to persuade jurors to reject the death penalty.

“Getting 12 out of 12, that’s the law, and trying to size up whether that’s likely or possible or probable is a big part of the decision,” Perrilloux said, adding that he has unsuccessfully sought a death sentence more times than he has prevailed.

Perrilloux said he has not yet had the chance to speak face-to-face with the victims' families, whose opinion is a major factor. Perrilloux said he usually explains to families the length of the process and has had many families say “no.”

Perrilloux has seen two extremes of the death penalty.

The most recent Louisiana death row execution, in 2010, involved a Livingston Parish case. Gerald Bordelon, who waived his rights to an appeal after he was convicted of kidnapping and killing his 12-year-old stepdaughter, Courtney LeBlanc. Bordelon, 47, was executed by lethal injection.

More recently, Perrilloux was at the center of a high-profile death row appeal that ended only in December when he offered a 25-year plea deal to Michael Wearry, who for years maintained he was innocent of the 1998 killing 16-year-old Eric Walber, an honors student and football player who was robbed, beaten and run over with his own car after he had finished his pizza delivery shift on April 4, 1998.

Wearry successfully appealed his case all the way to the U.S. Supreme Court, and the victim’s mother sat through dozens of hearings during the nearly 20-year ordeal.

Ken Levy, a criminal law professor at LSU, said district attorneys are also often considering the potential costs associated with a lengthy appeals process and a decline in public opinion about the death penalty, particularly in light of high-profile death row exonerations in recent years.

“There are legal considerations, but there are also political considerations and strategic considerations,” Levy said.

Levy said he does not believe the death penalty is viable in the Theriot case, given the mental health issues that are clearly documented for Theriot.

“If this had been a cold-blooded, premeditated killing of five different people, including family members, that seems to be very different and a much stronger case for the death penalty,” Levy said.

In Theriot’s case, his attorney may decide to pursue an insanity defense, whereby they would claim Theriot did not know right from wrong at the time of the crime and is, therefore, not guilty. Schizophrenia, which Theriot reportedly has, is one of the most common mental illnesses to qualify for that defense, Levy said.

But he said that the prosecutors may still end up seeking capital punishment, given the hideousness of the crime.

“This is as bad a crime as you can imagine, so they may in the end want to make a statement,” Levy said.

The case has been allotted to 21st Judicial District Judge Robert Morrison III, Perrilloux said. Should he decide to pursue the death penalty, the case would be reallotted.

Perrilloux said Theriot will continue to be held in the Livingston Parish Detention Center.

Follow Caroline Grueskin on Twitter, @cgrueskin.