A jury has found a Michigan mother guilty of involuntary manslaughter for failing to stop her son from carrying out a deadly school shooting.
Jennifer Crumbley, 45, is the first US parent convicted of manslaughter over a mass shooting carried out by their child.
Prosecutors accused her of being negligent in allowing her son to have a gun, and ignoring warnings signs.
Her husband, James, is facing a separate trial on the same charges.
He has pleaded not guilty.
Their son, now 17, is serving life in prison for killing four classmates at Oxford High School in Michigan on 30 November 2021.
Seven people were also injured in the shooting.
The judge, speaking to jurors, said this was likely "the hardest thing you've ever done".
Ms Crumbley appeared emotionless and stared straight down as the verdict was read in Oakland County court on Tuesday.
She was charged with four counts of involuntary manslaughter, each carrying a maximum sentence of 15 years.
Some relatives of those killed in the shooting expressed relief over the verdict.
"The People spoke!" Buck Myre, the father of Tate Myre, a 16-year-old killed in the shooting, told the BBC in a statement.
"You can agree or disagree with the people, but this is how the system is supposed to work."
The question at the heart of the trial was whether the mother could have foreseen and prevented the deadly crime.
Ms Crumbley and her husband James bought the gun their son used just days before the shooting.
They were charged by police within days of the killings. Police had to search for the pair and found them in an industrial building in Detroit following a tip from the public.
For more than two years they have been kept in a county jail, unable to make bail.
Initially, the parents were supposed to be tried together but in November sought separate trials. James Crumbley is scheduled to go on trial in March.
At her trial, prosecutors presented evidence that Ethan Crumbley had wanted mental health help and complained of hallucinations, but said his parents did not get him treatment. Ms Crumbley said on the stand that she did not think her son had mental health problems.
The morning of the shooting, the parents cut short a school meeting about a disturbing drawing their son had made to go to work and declined to take the then 15-year-old home.
School officials sent him back to class without checking his backpack, which contained a gun.
Just hours later, he killed Hana St Juliana, 14, Myre, 16, and Madisyn Baldwin and Justin Shilling, both 17.
Some experts have suggested the cases against the Crumbleys could lead to more charges for parents of children who commit mass shootings.
Stephen J Morse, a professor of law and psychiatry at the University of Pennsylvania, said he disagreed with the verdict, arguing that because Ethan Crumbley had pleaded guilty, he was the only one responsible for the shooting.
"I understand that she was not necessarily the best mother in the world, but this is not a crime," he said.
Mr Morse said he believed the decision could set a bad precedent, causing courts to look for "scapegoats" in similar situations.
Others say this case was so unusual that it is unlikely to have wider ramifications.
"I don't fear that this is going to open the floodgates to parents being charged in a run of the mill case, if there is such a thing," said Frank Vandervort, a University of Michigan clinical professor of law.
"I think the facts of this case are so unique and sort of extreme."
Prosecutors attempted to make the same case during the two-week trial, alleging Ms Crumbley ignored her son's pleas for help despite expressing concern about him in private messages.
They showed messages between Ms Crumbley and a man she had an affair with in which she said - before attending the school meeting on the day of the shooting - that she was afraid her son would do "something dumb".
When she took the stand in her own defense at her trial, Ms Crumbley sought to put the blame on her husband for the gun purchased for their son.
She told jurors that her husband brought their son to a gun store the day after Thanksgiving to buy him a handgun as a gift.
She said she "didn't feel comfortable" being responsible for securing the gun and left James Crumbley manage it.
Ethan Crumbley never took the stand, because he was expected to invoke his Fifth Amendment right against self-incrimination and refuse to testify.
Families of the victims have expressed frustration that school officials have not faced the same legal consequences as Mr and Ms Crumbley.
"Why isn't the system allowing the people to decide when it comes to the failures at the school?" Mr Myre told the BBC on Tuesday after the verdict.
"Is our government under a different set of rules?"
An independent investigation published last year alleged multiple failures from the school system, including allowing Ethan to return to class without checking his backpack.
The school district has pledged to review and improve its practices and policies in response to the report.