In a landmark case, his mother Jennifer Crumbley, 45, was found guilty of four counts of manslaughter – one for each victim – in February this year.
After prosecutors argued Ethan’s father also bore responsibility because he and his wife gave their son the gun and ignored signs of violence, James Crumbley, 47, was convicted on Thursday.
The Crumbleys were the first parents to be charged with manslaughter in a child’s school shooting in a country where such incidents are relatively common.
Gun safety experts hope the Crumbley trials serve as a wake-up call for parents to secure weapons in their homes, with 75% of school shooters getting guns from home, according to government research.
“This is a very egregious and rare, rare set of facts,” prosecutor Karen McDonald told the jury on Wednesday.
Ms McDonald said James Crumbley repeatedly ignored warning signs his son was deeply disturbed, did not get him help, and did not do enough to safely store the firearm in the family home.
“He did nothing over and over and over again,” she added.
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Ms McDonald also presented texts Ethan sent to a friend and journal entries in the months before the shooting, in which he talked about wanting medical help and hearing voices, but he was worried his parent would be “pissed”.
On one occasion, according to a text message to a friend, Ms McDonald said Ethan had asked James Crumbley to take him to the doctor, but his dad “gave me some pills and told me to suck it up”.
Defence lawyer Mariell Lehman argued James Crumbley could not have possibly foreseen his son would carry out a mass shooting.
“James had no idea that his son was having a hard time,” Ms Lehman told jurors, saying no evidence had been presented that James knew the contents of his son’s text messages or journal.
‘The thoughts won’t stop – help me’
According to prosecutors, James Crumbley bought the gun used in the attack four days before the shootings.
On the morning of the shootings, on 30 November, a teacher found drawings by Ethan showing a handgun, a bullet and a bleeding figure next to the words “blood everywhere”, “my life is useless”, and “the thoughts won’t stop – help me”.
Summoned to the school that same morning, the Crumbleys were told Ethan needed counselling and they needed to take him home, according to prosecutors.
But the couple wouldn’t take their son, prosecutors said, and did not search his rucksack or ask him about the gun.
Both of the Crumbleys challenged that account in their trials, saying teachers in the meeting mutually agreed Ethan could remain in school that day and at no point did they think he posed a danger.
Ethan was returned to class and later walked out of a bathroom with the gun and began firing, according to prosecutors, killing 14-year-old Hana St Juliana, 16-year-old Tate Myre, 17-year-old Madisyn Baldwin, and 17-year-old Justin Shilling and injuring seven other people.
Jennifer Crumbley is set to be sentenced on 9 April.
Much has been said about the students whose protests have gripped America this past week.
Their cause has been framed in polarising ways. A violent Hamas-sympathising mob? Or peace activists striving for equality?
Within a frenzied spectrum of views and noise, one young student sat down with me for a conversation.
Aidan Doyle, 21, is a philosophy and jazz double major at the University of California in Los Angeles (UCLA).
He was arrested early on Thursday morning for being part of an encampment at the university.
He told Sky News he was shocked that the police arrested so many student protesters, despite not intervening in an attack on the protesters by a pro-Israeli group the day before.
He said his arrest had not deterred him from continuing his protest, which he likened to the Vietnam War demonstrations of the 1960s.
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Mr Doyle rejected the notion, from President Biden, that the protests are not peaceful.
“Graffiti, putting posters up, that’s all peaceful,” he said, commenting on the president’s statement from the White House.
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“I also think that President Biden needs to actually take some introspection and realise that maybe the reason so many of these protests are happening is partially due to him.”
Mr Doyle added: “Protests in general are part of the American spirit. They’re part of being an American. And if we were to just stand around in circles and sing and dance, and pretend everything was fine, then nothing would change and nobody would care at all.
“Part of a protest is causing disruption and causing at least a minor level of chaos that is, again, not violent but that actually disrupts things.”
He denied any accusations of antisemitism, but conceded there is a spectrum of opinion within the movement.
“If you’re going to criticise a movement, I think you have to look at the movement’s goals and their mission, not what fringe members of the group say or do.
“You have to actually look at what we say, what the organisers say, and what is in the mainstream, and what our mission and our goal is: the peace and prosperity of the Palestinian people.”
Asked if he believed in Israel’s right to exist as a country, he said: “I think Jewish sovereignty is incredible. I think it’s an amazing thing.”
He added: “I think that if there is a country for Jewish people that protects the Jewish people, that is of utmost importance, especially with the vile and rampant antisemitism that exists across the world that I see every day and that I try and combat as much as possible.
“But doing that and then simultaneously repressing another group of people, dehumanising them and brutalising them, then the question of whether your state has the right to exist becomes secondary.”
Students, charged and released with a date in court, are here now to collect their belongings. They’re missing bags, belts, shoes, all lost in the chaos of the night before.
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From the very heart of the protest encampment, our cameras had captured the chaos.
Officers moving in. Tear gas and rubber bullets to disperse. Stun grenades to disorientate.
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They were scenes which have stirred an already fevered debate about Israel and Gaza, yes, but about much more too. About America, about policing, and about free speech too.
President Biden said yesterday: “Vandalism, trespassing, breaking windows, shutting down campuses, forcing the cancellation of classes and graduations – none of this is a peaceful protest.”
‘Wrong’ say the protesters. Their movement, they say, is the very essence of protest; of civil disobedience which is threaded through US college campus history.
They reject any notion that they are threatening or violent. Yet the deeply divisive history of the Israel-Palestine conflict ensures that the beholder will so often be offended by the actions of the other side.
It was the students perceived antisemitism through their pro-Palestinian slogans which had drawn a group of pro-Israel protesters to the encampment earlier in the week.
The chaos of that night was reflected in a statement by the university’s student radio station which has been covering every twist.
“Counter protestors used bear mace, professional-grade fireworks and clubs to brutalize hundreds of our peers, UCLA turned a blind eye. Police were not called until hours into the onslaught and stood aside for over an hour as counter-protestors enacted racial, physical and chemical violence,” the statement from the UCLA Radio Managerial team said.
Watching the clear-up after the nighttime police sweep of the protesters I spotted two people embracing. A young man and an older woman.
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Professor recalls violent arrest at protest
It turned out to be a thread of history. One was a student who’d been arrested the night before.
The other was a student from a past time. Diane Salinger had been at New York’s Columbia University in 1968, at protests which now form a key chapter in American history.
“I’m so proud of these people here. I’m so proud,” she told me.
“You know the civil unrest of the students back in ’68 and it continued for several years, it actually changed the course of the Vietnam War and hopefully this is going to do the same thing.”
But then, back at the police station, a conversation that hints at the wider challenges for America.
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‘Tom’ is a protester who wanted to remain anonymous – a graduate who feels politically deserted in his own country. For him, no government is better than any on offer.
“The problem with our system is that we can’t rely on the police, we can’t rely on the military to keep us safe.
“When we need to make our voices heard, we need to make them heard, and the only way to do that without being repressed is by keeping each other safe and I think that last night and the last few months have really exemplified that,” he told me.
These protests are about more than Gaza. They are aligning a spectrum of dissent.
A scuba dive boat captain has been jailed for four years for criminal negligence over a fire that killed 34 people.
Captain Jerry Boylan was also sentenced to three years supervised release by a federal judge in Los Angeles, California.
The blaze on the vessel named Conception in September 2019 was the deadliest maritime disaster in recent American history.
Boylan was found guilty of one count of misconduct or neglect of ship officer last year.
The charge is a pre-Civil War statute, known colloquially as seaman’s manslaughter, and was designed to hold steamboat captains and crew responsible for maritime disasters.
In a sentencing memo, lawyers for Boylan – who is appealing – wrote: “While the loss of life here is staggering, there can be no dispute that Mr Boylan did not intend for anyone to die.
“Indeed, Mr Boylan lives with significant grief, remorse, and trauma as a result of the deaths of his passengers and crew.”
The Conception was anchored off Santa Cruz Island, 25 miles south of Santa Barbara, when it caught fire before dawn on the final day of a three-day voyage, sinking less than 30 metres from the shore.
Thirty-three passengers and a crew member died, trapped below deck.