A prosecutor filed involuntary manslaughter charges Friday against the parents of a 15-year-old accused of killing four students and wounding seven other people at a Michigan High School.

James and Jennifer Crumbley were charged with four counts each of involuntary manslaughter.

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Authorities have said Ethan Crumbley opened fire shortly before 1 p.m. Tuesday at Oxford High School, roughly 30 miles (50 kilometers) north of Detroit. Seven students and a teacher were shot before Crumbley surrendered to sheriff’s deputies.

Three of the students died Tuesday. The fourth died Wednesday at a hospital.

The semi-automatic gun used in the shooting was purchased legally by Crumbley’s father last week, according to investigators.

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“The parents were the only individuals in the position to know the access to weapons,” Oakland County prosecutor Karen McDonald said Thursday. The gun “seems to have been just freely available to that individual.”

She said then that the parents’ actions went “far beyond negligence.”

Ethan Crumbley has been charged as an adult with two dozen crimes, including murder, attempted murder and terrorism.

William Swor, a defense lawyer who is not involved in the case, said charging the parents would require a “very fact-intensive investigation.”

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“What did they know and when did they know it?” Swor said. “What advance information did they have about all these things? Did they know anything about his attitude, things of that nature. You’re talking about a very heavy burden to bring on the parents.”

Just over half of U.S. states have child access prevention laws related to guns, but they vary widely. Gun control advocates say the laws are often not enforced and the penalties are weak.

“Our laws haven’t really adapted to the reality of school shootings and the closest we have are these child access prevention laws,” said Kris Brown, president of the Brady gun control advocacy group.

In 2000, a Flint-area man pleaded no contest to involuntary manslaughter and was sentenced to two years in prison. A 6-year-old boy who was living with him had found a gun in a shoebox and killed a classmate at school.

In 2020, the mother of an Indiana teen was placed on probation for failing to remove guns from her home after her mentally ill son threatened to kill students. He fired shots inside his school in 2018. No one was injured but the boy killed himself.

In Texas, the parents of a student who was accused of killing 10 people at a school in 2018 have been sued over his access to guns.

Meanwhile, dozens of schools in southeastern Michigan canceled classes Thursday due to concerns about threatening messages on social media following the Oxford shooting. Some schools stayed open with a larger police presence.