CORY WILLIAMS and MIKE HOUSEHOLDER

PONTIAC, MI. A teenager pleaded guilty Monday to terrorizing and first-degree murder in a shooting at a Michigan school that killed four students and focused attention on the boy’s home life and his parents’ alleged role in the tragedy.

Ethan Crumbley pleaded guilty to all 24 charges nearly a year after the attack at Oxford High School in southeast Michigan. In the gallery, some of the victims’ relatives wept as Assistant District Attorney Mark Kist described the crimes.

“Yes,” he said, looking down and nodding in the affirmative when asked if he had decided to “knowingly, deliberately and intentionally” shoot the other students.

Prosecutors said no deals had been made ahead of Monday’s plea. A first-degree murder conviction usually carries an automatic life sentence in Michigan, but teenagers have the right to a hearing where their attorney can seek a reduced sentence and the possibility of parole.

The teenager abandoned his intention to plead insanity and repeatedly admitted that he understood the possible punishments. Deborah McKelvey, his court-appointed guardian, told Oakland District Court Judge Kwame Rowe that she met with him Thursday at the county jail and believes he fully understands the consequences.

Ethan, now 16, had no disciplinary problems at the school, about 30 miles north of Detroit, but his behavior earlier on the day of the mass shooting raised flags.

The teacher found a picture of a gun pointed at the words: “Thoughts won’t stop. Help me.” There was an image of a bullet with the words, “Blood everywhere.”

James and Jennifer Crumbley refused to take their son home on Nov. 30, but were told to take him to counseling within 48 hours, according to investigators.

Ethan brought a Sig Sauer 9mm pistol and 50 rounds of ammunition to school that day in a backpack. He went into the bathroom, took out a weapon, and then shot students in the hallway. A few minutes later, deputies burst in and he surrendered without resistance.

The day before, the teacher had seen Ethan looking for ammunition on his phone. The school contacted Jennifer Crumbley, who told her son in a text message, “Lol. I’m not mad at you. We need to learn not to get caught,” the prosecutor’s office said.

In addition, the elder Crumbley was charged with involuntary manslaughter. They are accused of giving Ethan a gun and ignoring his need for mental health treatment. Parents have rarely been charged in school shootings, although the weapons usually come from the home of a parent or close relative.

Prosecutors revealed earlier this year that Ethan had hallucinations of demons and was fascinated by weapons and Nazi propaganda.

“Simply put, they created an environment in which their son’s violent tendencies flourished. They knew that their son had problems, and then they bought him a gun,” the prosecutor’s office said.

The Crumbles said they were unaware of Ethan’s plan to carry out a school shooting. They also dispute that the gun was easily seized at home.

Madisyn Baldwin, Tate Myr, Hannah St. Juliana, and Justin Schilling were killed, and six students and a teacher were wounded. In addition to the counts of first degree murder and terrorism resulting in death, Eaton pleaded guilty to seven counts of assault with intent to murder and 12 counts of possession of a firearm in the commission of a felony.

A judge set a hearing for Feb. 9 to determine whether he will be sentenced to life in prison without parole or receive a reduced sentence because of his age and the chance of parole. His lawyers will be able to argue various mitigating circumstances, including family life and mental health. The prosecutor’s office did not give a signal in court whether they would advocate for a postponement of the sentence.