When a child commits a mass shooting, are parents to blame?

They supplied the weapon. Should the parents of a 15-year-old mass shooter be criminally responsible for the deaths of four high school students?

Almost every day, Steve and Ai St Juliana wear the same sweatshirt, each adorned with a flower in the top left corner.

The matching outfits have brought a speck of colour to a life that the two said has become "duller" since the death of their empathetic and athletic 14-year-old daughter Hana, which means flower in Japanese. The five petals of the flower represent the family members, with Hana's name in the centre written in Japanese.

Hana was the youngest of four students killed at Oxford High School in 2021 when 15-year-old Ethan Crumbley opened fire. Tate Myre, 16, and Madisyn Baldwin and Justin Shilling, both 17, were also killed in the attack. Seven others, including a teacher, were wounded.

The school shooting, the worst in the state's history, rocked Oxford Township, a 22,000-person suburb north of Detroit.

"She was always laughing, always causing people to laugh," Hana's father, Steve St Juliana, told the BBC at their family home in Ortonville, Michigan.

"Every day without her really is a new struggle. She was the heart and soul of the family."

On Friday, more than two years after the shooting, a judge sentenced Crumbley, now 17, to life in prison without the possibility of parole, the maximum sentence.

But the case has raised questions about who else can be held accountable for a mass shooting when a child pulls the trigger. It was Crumbley's parents who gifted him the weapon he used just days before the attack, and they also attempted to flee after being charged with involuntary manslaughter.

James and Jennifer Crumbley have pleaded not guilty and will face two separate trials in 2024. It marks the first time parents will face manslaughter charges - punishable by up to 15 years in prison - for their child's role in a mass school shooting, experts told the BBC.

The school also faces criticism that it could have prevented the tragedy.

Before the Oxford shooting, Kayla LeMieux had not thought about Ethan Crumbley since he was a nine-year-old boy living across the street from her in nearby Lake Orion, Michigan.

Ms LeMieux worked with Ethan's mother, Jennifer, at a restaurant in 2015 and was close with the Crumbley family after they moved into a nearby apartment in Lake Orion before settling in Oxford.

She said Mr and Mrs Crumbley would frequently leave Ethan home alone when he was nine for hours while they would go into town to drink.

During this time, Ethan would sometimes wander over to her house, where her interactions with him proved troubling, she said.

"He was very monotone, very distant, manipulative. He lied a lot," Ms LeMieux said.

She recalled one time when she watched him take a bird's nest down from a tree and then stomp on it.

The behaviour raised alarm bells for Ms LeMieux and her boyfriend.

"We would say, 'He's going to kill someone one day,'" she said.

In court, Ethan Crumbley's attorneys have painted a similar picture of the boy's childhood, calling a psychological expert who said he was a "feral child" who was neglected by his parents and suffered from mental illness.

In the case against his parents, prosecutors have also argued the Crumbleys were at times more focused on their extramarital affairs and spending time with their horses than tending to their son's declining mental health.

Ms LeMieux said Mr and Ms Crumbley's parenting eventually led her to call Child Protective Services.

"Ethan was so neglected. He was just a baby. I was worried for him. That's not a way for a kid to grow up," she said.

But holding the Crumbleys partly responsible for the attack could prove challenging in court - especially since the case appears to be one of the first of its kind - experts told the BBC.

US law is generally designed only to hold individuals responsible for their own actions, legal experts said.

Still, several elements of the Crumbley case likely compelled Oakland County Prosecutor Karen McDonald to bring charges against the parents.

For one, the family purchased Ethan the handgun he used just days before the shooting as an early Christmas present and failed to properly secure the weapon, prosecutors allege.

The parents also refused to take him home from school on the day of the shooting as school officials suggested, after finding Ethan's drawings of a gun and bloody figures.

Still, prosecutors will have to prove that it was foreseeable to the parents that their disturbed 15-year-old son would carry out the shooting, said Stephen J Morse, a professor of law and psychiatry at the University of Pennsylvania.

"It would be bizarre to think it was reasonably foreseeable that he would engage in mass murder."

Caitlin Cavanaugh, an associate professor in Michigan State's School of Criminal Justice, said popular culture portrays parents as principally responsible for child delinquency, but she said a host of factors can lead someone to grow up to become violent.

"Generally it's not appropriate to suggest that parents shoulder full responsibility for their children's crimes," she said. "But, every case is different, and certainly understanding a child's home background can help us understand their actions."

But while the Crumbleys may be the first to face manslaughter charges for a mass shooting their child committed, prosecutors are increasingly trying to hold third parties responsible for others' homicides, Mr Morse said.

In November, the father of a man accused of killing seven at a Fourth of July parade in Highland Park, Illinois pleaded guilty to reckless conduct for helping his adult son obtain the gun used in the attack.

The same month, the mother of a six-year-old boy who shot his first-grade teacher was sentenced to 21 months in prison in Virginia after pleading guilty to child neglect.

The St Juliana family said they were relieved prosecutors were seeking to hold Crumbley's parents accountable for their "appalling" negligence.

"They need to be made an example of," said Steve St Juliana. "But nothing that is done to them is going to bring our daughter back."

While the parents of Ethan Crumbley have faced mounting scrutiny, many have also laid blame on the Oxford Community Schools district.

In November, a group of around 30 Oxford High School students walked out of class to demand the resignation of several school board officials.

They also asked for more trauma services at school and a memorial to commemorate the victims.

A month earlier, an independent firm, Guidepost Solutions, had released its final report on the school's response to the shooting. The probe alleged multiple failures from school officials, who failed to check Crumbley's backpack for weapons after teachers discovered his disturbing, violent drawings. He would begin shooting students within hours after being sent back to class.

It also found the school board discouraged staff from cooperating with investigators.

"The report is very damning. It makes it very clear that from beginning to end, [the school] made errors over and over and over again," Mr St Juliana said.

"But they've done everything in their power to run from taking any responsibility."

The Oxford Community Schools district did not respond to a request for comment from the BBC.

Mr St Juliana and other parents of those killed and injured in the shooting have filed lawsuits against the district.

In March, an Oakland County judge dismissed several civil suits against the school, ruling that the district and its employees had governmental immunity, writing that Crumbley himself was "the one most immediate, efficient, and direct cause of the injury or damage".

Still, the St Julianas have been working to make sure the memories of their daughter and the other victims will not be forgotten, raising money for a memorial garden in a popular local park. Mr St Juliana said he wants to plant four cherry trees and small mementos from each of their lives.

"It's a reminder to the community to not forget and to not let your guard down," he said.