A Southern Maryland judge outraged that two girls tormented a 16-year-old autistic boy nevertheless ruled Thursday that the older of the two should not be tried as an adult.

St. Mary’s County Circuit Judge David Densford moved the case against Lauren A. Bush, 17, from adult court, where the Chopticon High School junior could have faced up to 80 years in prison, to the juvenile system, where she faces a maximum of four years.

Bush and a 15-year-old friend used a cellphone to record the abuse, which included holding a butcher knife to the boy’s throat and luring him onto a partially frozen pond, then refusing to help when he fell in.

“The conduct on the DVDs, and her statements to the police are outrageous. There is a lack of empathy . . . a dramatic lack of empathy,” Densford said. “You look at them and say, ‘Why would any human being treat another person like this?’ ”

But he also acknowledged evidence that Bush suffered trauma as a child and multiple concussions as a Chopticon cheerleader. And he concluded that it didn’t make sense to send her to an adult prison.

“This outrageousness, this ugliness does not make it the sort of criminal activity that should subject Lauren Bush to the Jessup women’s prison,” Densford said.

The decision to prosecute Bush as a juvenile marked a defeat for county law enforcement authorities, who wanted Bush to be punished as severely as possible in the high-profile case.

Instead of facing possible convictions in adult court on two first-degree assault charges, the teenager pleaded guilty in juvenile court Thursday to distribution of an obscene video and a misdemeanor charge of second-degree assault.

Bush said little and teared up for much of the court proceedings. Shackled at her feet and dressed in sneakers, khakis and an oversize gray sweatshirt, she looked far younger than 17.

Her father, Larry Bush, briefly testified and said his daughter was sorry. He told the court that Lauren has apologized once to the boy, but it was unclear when.

“We’re 100 percent committed to getting Lauren all the help she needs,” he said.

John Pleisse, the county prosecutor in the case, could not be reached to comment after the hearing.

The victim’s parents, who had forced themselves to watch the videos earlier this month, were divided about how they felt about the judge’s decision. The boy’s mother said she’d been persuaded that Bush deserved rehabilitation in a juvenile facility. But his father, a federal government contracting analyst, disagreed.

“I think she’s a danger to herself and to the community,” he said.

Bush’s accomplice, a 15-year-old girl, was sentenced in juvenile court in April to a maximum of six years in a secure juvenile facility, having pleaded guilty to second-degree assault and displaying an obscene photograph of a boy. (Because the 15-year-old was originally charged as a juvenile and never named by law enforcement authorities, The Washington Post is not identifying her.)

The girls’ arrest in March and details about their crimes — which also included trying to run the boy over with a car and encouraging him to try to have sex with his family’s dog — prompted outrage online, in news stories worldwide and disgust within Southern Maryland.

All three teenagers knew each other at Chopticon High, and the boy, who is high-functioning, considered the girls his friends. Sheriff’s deputies learned about the abuse in early March after a Chopticon student tipped them off that the 15-year-old’s cellphone contained the incriminating video recordings. The confiscated videos led to the girls’ arrest.

At Thursday’s hearing, the judge cited the 32-page police report and read aloud some of Bush’s statements after she was caught by authorities. Some of her remarks included:

“We should have erased the videos,” and “We were stupid. We’ll be smarter after this, or locked behind bars.” And after authorities arrived at her home to arrest her, she told them: “I have a project tomorrow. I can’t go to jail.”

The judge was steamed. “If the conduct isn’t outrageous enough, the comments afterward make it worse,” he said. “This is not an empathetic or remorseful person from the totality of the evidence.”

Bush’s attorney, Brian Thompson, said that one reason the judge ruled in Bush’s favor is that she voluntarily committed herself to a Montgomery County juvenile detention center last month rather than remain under house arrest. The judge cited her progress report from the juvenile center, which indicated that she was a “low-to-moderate” risk to the community, and the state’s juvenile services department’s recommendation that she should get treatment in a juvenile facility, not in an adult prison.

“She should have been treated as a juvenile from Day One — she’s been publicly and permanently named and turned into a pariah as a result of this, and that never goes away,” Thompson said. “I think the judge made a brave decision in light of the public outcry. But from a strictly legal perspective, it was a straightforward case.”