The parents of a Michigan school shooter were each sentenced to at least 10 years in prison Tuesday for failing to take steps that could have prevented the killing of four students in 2021.

Jennifer and James Crumbley are the first parents convicted in a U.S. mass school shooting. They were found guilty of involuntary manslaughter after prosecutors presented evidence of an unsecured gun at home and indifference toward the teen’s mental health.

Ethan Crumbley drew dark images of a gun, a bullet and a wounded man on a math assignment, accompanied by despondent phrases. Staff at Oxford High School did not demand that he go home but were surprised when the Crumbleys didn’t volunteer it during a brief meeting.