PONTIAC, Mich. (AP) 鈥 A teenager pleaded guilty Monday to terrorism and first-degree murder in a Michigan school shooting that killed four students and may be called to testify against his parents, who've been jailed on manslaughter charges for their alleged role in the tragedy.

Ethan Crumbley, 16, pleaded guilty to all 24 charges, nearly a year after the attack at Oxford High School in southeastern Michigan. In the gallery, some relatives of the victims wept as assistant prosecutor Marc Keast described the crimes.

鈥淵es,鈥 Crumbley replied, looking down and nodding in affirmation, when asked if he 鈥渒nowingly, willfully and deliberately鈥 chose to shoot other students.

The prosecutor's office said no deals were made ahead of Monday's plea. A first-degree murder conviction typically brings an automatic life prison sentence in Michigan, but teenagers are where their lawyer can argue for a shorter term and an opportunity for parole.

鈥淲e are not aware of any other case, anywhere, in the country where a mass shooter has been convicted of terrorism on state charges,鈥 Oakland County Prosecutor Karen McDonald said.

The teenager withdrew his intent to pursue an insanity defense, and repeatedly acknowledged under questioning by Judge Kwame Rowe that he understands the potential penalties.

His parents, James and Jennifer Crumbley, are jailed accused of making the gun accessible to their son and ignoring his need for mental health treatment. Ethan Crumbley's lawyer, Paulette Michel Loftin, said it's possible he could be called upon to testify against them. She said they're under a no-contact order, and he has not spoken to his parents.

Ethan Crumbley was 15 at the time of the shootings and had no discipline issues at the school, roughly 30 miles (50 kilometers) north of Detroit, but his behavior earlier that day raised flags.

A teacher had discovered a drawing with a gun pointing at the words: 鈥淭he thoughts won鈥檛 stop. Help me.鈥 There was an image of a bullet with the message: 鈥淏lood everywhere.鈥

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

Ethan Crumbley had brought a 9mm Sig Sauer handgun and 50 rounds of ammunition to school in his backpack that day. He went into a bathroom, pulled out the weapon and began shooting. Within minutes, deputies rushed in and he surrendered without resistance.

A day earlier, a teacher had seen Ethan Crumbley searching for ammunition on his phone. The school contacted Jennifer Crumbley, who told her son in a text message: 鈥淟ol. I鈥檓 not mad at you. You have to learn not to get caught,鈥 the prosecutor鈥檚 office said.

Parents have rarely been charged in school shootings, though the guns used commonly come from the home of a parent or close relative. Jennifer Crumbley referred to the gun on social media as a 鈥淐hristmas present鈥 for her son.

Ethan Crumbley admitted under questioning Monday that his own money was used to purchase the gun, which his father bought for him on Nov. 26, a few days before the shooting. He also said the gun was 鈥渘ot locked鈥 in a container or safe the morning he took it to the school.

Sheriff Michael Bouchard told reporters Monday that Ethan Crumbley still had 18 rounds of ammunition when he was arrested.

鈥淚t鈥檚 my belief he would have fired every one of those had he not been interrupted by deputies going immediately in,鈥 said Bouchard who also called Ethan Crumbley 鈥渁 twisted and evil person.鈥

鈥淚 hope he gets life without parole,鈥 the sheriff added. 鈥淗e has permanently taken lives away from four lovely souls and he鈥檚 permanently affected many, many more.鈥

Prosecutors earlier this year disclosed that about demons and was fascinated by guns and Nazi propaganda.

"Put simply, they created an environment in which their son鈥檚 violent tendencies flourished. They were aware their son was troubled, and then they bought him a gun,鈥 prosecutors said in a court filing.

His parents said they were unaware of their son's plan to commit a school shooting. They also dispute that the gun was easy to grab at home.

Madisyn Baldwin, Tate Myre, Hana St. Juliana and Justin Shilling were killed, while six students and a teacher were wounded. In addition to the counts of first-degree murder and terrorism causing death, Ethan Crumbley admitted guilt to seven counts of assault with intent to murder and 12 counts of possessing a firearm in the commission of a felony.

The judge set Feb. 9 for the start of hearings to determine if he'll be sentenced to life without parole or get a shorter sentence due to his age, and a chance at release. His lawyers will be able to argue a variety of mitigating circumstances, including family life and mental health. Prosecutors didn鈥檛 signal in court if they will argue for a no-parole sentence.

Loftin said the teenager is remorseful: 鈥淗e's taking accountability for his actions,鈥 she said. As for the victims, she said 鈥淚 don't think there are any words that could make them feel any better.鈥

Meghan Gregory, whose son, Keegan, was hiding in a school bathroom with Justin Shilling when Shilling was fatally shot, told reporters after the hearing that it was tough to see Crumbley for the first time in person.

She said her son did not want to attend, but did ask for a link to the livestream so he could watch the hearing from afar.

鈥淗e struggles with the thought of being in the same room,鈥 Gregory said. 鈥淚 mean, he was held hostage by him for almost six minutes.鈥

Detroit attorney Ven Johnson, who is suing the Oxford school district and the Crumbley family on behalf of several victims鈥 families, said Monday鈥檚 plea 鈥渋s one small step forward on a long path towards obtaining full justice for our clients.鈥

鈥淲e will continue to fight until the truth is revealed about what went wrong leading up to this tragedy, and who, including Crumbley鈥檚 parents and multiple Oxford Community Schools employees, could have and should have prevented it,鈥 Johnson's statement said.

Wolf Mueller, another lawyer representing victims鈥 families, said it was 鈥減retty incredible to hear鈥 and 鈥渁 stunning development鈥 that Ethan Crumbley acknowledged he purchased the gun with his own money.

鈥淚t was cold-blooded what he did,鈥 Mueller said. 鈥淎nd, while he may have been dealt a bad set of cards with the parents, it鈥檚 still a choice that he made to do the harm and bring the tragedy to Oxford.鈥

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Williams reported from West Bloomfield, Michigan.

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