A Las Vegas teenager pleaded guilty as an adult Wednesday to felony charges that a prosecutor said could get him decades in prison for attacking a high school teacher and leaving her unconscious in a classroom a year ago.

The incident, which included allegations of sexual assault, left the teacher hospitalized with multiple injuries and focused attention on a sharp rise in violence at the time in the sprawling Clark County School District, the nation’s fifth-largest.

The Associated Press is not naming the defendant due to his age. Now 17, he pleaded guilty to attempted murder, attempted sexual assault and battery with a deadly weapon causing substantial bodily harm. His pleas avoided trial in Clark County District Court.

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Public defenders who represented the boy did not immediately respond to email messages form AP.

The prosecutor, Chief Deputy Clark County District Attorney William Rowles, confirmed the plea agreement. He told the Las Vegas Review-Journal that he intends to seek the maximum sentence of 55 years in prison at sentencing June 5.

Las Vegas police said the boy went to the teacher to talk about his grades before punching and choking her into unconsciousness and fleeing the classroom at Eldorado High School, a campus serving about 2,000 students. Another school employee found the teacher and summoned police and medical help.

The teacher later told investigators the teen approached her as she sat at her desk and choked her from behind with a rope or cord before pulling a bookcase and filing cabinet down upon her.

"I don’t know why I attacked her, she was good to me," a police arrest report quoted the student telling detectives.

The teen, who attended ROTC, was arrested about two hours later while his mother drove him back to campus for a corps award ceremony.