Ethan Crumbley sits in court on July 27 in Pontiac, Michigan.
CNN  — 

The teen gunman who killed four students at Oxford High School, is eligible for life imprisonment without parole – the harshest possible punishment in Michigan, a judge ruled Friday.

Ethan Crumbley, now 17, was 15 when he opened fire at the school on November 30, 2021. He has pleaded guilty to one count of terrorism causing death, four counts of first-degree murder and 19 other charges related to the deadly rampage.

Seven people, including a teacher, were also shot and survived.

Now, Crumbley is eligible for life in prison without the possibility of parole, Oakland County Circuit Court Judge Kwamé Rowe said Friday. The decision marks the latest court development in a nation still plagued by school shootings, with more than 50 recorded and 27 people dead so far this year.

The judge in Crumbley’s case considered the teen’s behavior both before the mass shooting and during his time in custody since his arrest, he said Friday.

“It’s clear to this court the defendant had an obsession with violence before the shooting,” Rowe said, citing Crumbley’s disturbing writings and documented violence against animals before the mass shooting.

Since his arrest, the judge said, Crumbley this year bypassed technical security on a jail tablet to watch graphic, violent content online.

Rowe said Crumbley’s rehabilitation in prison is unlikely because of his “obsession” with violence.

“If the defendant continues to be obsessed with violence in the jail, how can there be a possibility of rehabilitation?” the judge said.

Still, Crumbley’s fate remains uncertain, with his formal sentencing scheduled for December 8. While he is eligible for a life sentence without parole, Crumbley could still be given a life sentence – with the possibility of parole.

Shooting victims who survived the attack and family members of those killed are expected to give victim impact statements at the sentencing hearing in Pontiac, Michigan, before Rowe hands down Crumbley’s sentence December 8.

The killer’s parents also face charges

While Crumbley remains in jail awaiting sentencing, his parents are in jail awaiting trial. Jennifer and James Crumbley have both been charged with four counts of involuntary manslaughter.

Prosecutors have said they gave their son easy access to a gun and disregarded signs he was a threat. The parents allegedly ignored Crumbley’s request for mental health treatment after the teen said he needed help, according to an opinion written by a panel of judges in March.

The parents have argued the charges have no legal justification and they should not be held responsible for their son’s killings.

“There is no question that defendant’s home environment was not ideal,” Rowe said Friday.

“The court finds that the defendant’s parents frequently left him alone since an early age, that his parents frequently used alcohol and argued in front of the defendant, that his parents failed to take his mental health seriously, and that his father bought him the gun that he used in the school shooting,” the judge said.

Rowe acknowledged the shooter’s family and home environment are mitigating factors on his behalf.

“Nevertheless, the court finds that the defendant is the sole participant in the underlying crime,” Rowe said. “He methodically walked through the school, picking and choosing who was going to die. He wanted to kill the innocent.”

What led up to the judge’s ruling

Oakland County prosecutors and Crumbley’s defense team presented witness testimony and evidence over the summer at a so-called Miller hearing – one required by law in which prosecutors seek a life sentence without the possibility of parole for a minor defendant.

Prosecutors argued the premeditation of Crumbley’s attack was justification for a finite life sentence. They played audio messages in court in which the teen said, “I am going to be the next school shooter,” and he would “have so much fun.”

In seeking a prison sentence with parole eligibility, defense attorney Paulette Loftin asked the judge to consider mitigating factors like Crumbley’s difficult home life and ignored pleas to his parents for mental health treatment.

Loftin also asked the court to give Crumbley a chance at rehabilitation and to allow a parole board to determine his progress years from now.

Oakland County prosecutor Karen McDonald conceded Crumbley’s parents were negligent during her closing argument at the hearing but said that doesn’t outweigh the act and other factors.

“We have to deal with the darkness and the violence, and we have to accept that it happened. And we can also say we wish he had a better upbringing. But we’re not going to ignore facts – and the facts are that he had a choice,” the prosecutor said.

“He had many opportunities. He plotted, he planned, he showed none of the mitigating factors and evidence that you see in hundreds of other juvenile life without parole cases,” McDonald said.

Students and faculty who survived the shooting testified about their experience coming face to face with the shooter at the hearing. Expert witnesses from both sides gave dueling testimony about the effects of the shooter’s difficult home life, his mental health and how likely it is that he can be rehabilitated in prison.

CNN’s Ashley R. Williams contributed to this report.