Ethan Crumbley was 15 years old when he opened fire at Oxford High School on November 30, 2021, with a semi-automatic handgun his father had bought him as a Christmas gift days earlier. Six other students and a teacher were also wounded.
Crumbley's parents have also been charged with involuntary manslaughter in connection with the shooting, in one of the first US cases that seeks to hold parents accountable for their child's school shooting.
Oakland County Circuit Judge Kwame Rowe on Friday rejected defence lawyers' request for the possibility of parole, calling the massacre a "true act of terrorism".
"This act involved extensive planning, extensive research, and he executed on every last one of the things he planned," Rowe said.
Crumbley addressed the judge briefly, taking responsibility for his actions and promising to work on becoming a better person, regardless of his sentence.
"All I want is for the people I hurt to have a final sense of culpability that justice has been served," he said.
Crumbly was denied possibility of parole for what the judge described as a "true act of terrorism". (AP PHOTO)
Over the course of more than four hours, relatives of the victims and survivors of the attack detailed their daily struggles to move past the shooting.
Some students said they grow uncontrollably anxious in crowded or enclosed spaces, others described having trouble maintaining friendships or attending class.
Steve St. Juliana, whose 14-year-old daughter Hana was killed, remembered her as a talented, athletic girl who spoke Japanese, earned straight A's and crafted homemade jewellery.
"I will never think back fondly on her high school and college graduations," he said tearfully. "I will never walk her down the aisle as she begins the journey of starting her own family. I am forever denied the chance to hold her or her future children in my arms."
Kylie Ossege, a student who was shot through the shoulder and suffered a spinal injury, described lying on a blood-soaked carpet trying to reassure Hana, who was groaning beside her, as they waited desperately for help.
"Fifteen minutes of lying there absolutely helpless - 15 minutes of lying in a pool of my own blood," she said. "Fifteen minutes of hearing Hana St. Juliana's last sounds while stroking her hair."
As the witnesses spoke, Crumbley sat unmoving in an orange prison jumpsuit, his head and eyes cast downward - even when some speakers demanded he look at them.
In addition to Hana, the other students killed at Oxford High were Madisyn Baldwin, 17, Tate Myre, 16, and Justin Shilling, 17.
Crumbley pleaded guilty last year to two dozen counts, including one count of terrorism causing death and four counts of first-degree murder.
During a hearing in August to determine whether he should be eligible for parole, prosecutors introduced evidence showing that Crumbley made several chilling statements before the attack, including an audio recording in which he predicted he would "have so much fun" shooting his classmates.
Prosecutors have accused his parents, James and Jennifer Crumbley, of gross negligence for knowing their son was too young and troubled to own a gun but giving him a weapon anyway.
