Ethan Crumbley pleaded guilty in 2022 to two dozen counts, including four of first-degree murder, and last month was sentenced to life in prison without parole.
Jennifer Crumbley and her husband James Crumbley were being tried separately after being charged with four manslaughter counts in late 2021.
Legal experts have said that the parents' trial, which appears to be the first of its kind, breaks new legal ground.
"Rarely are high school shooters going out and buying guns from a gun store," Horwitz said.
Ethan Crumbley was returned to class and later walked out of a bathroom with the gun and began firing, prosecutors say.
Persons:
Brad Brooks, Jennifer Crumbley, Ethan, Ethan Crumbley, James Crumbley, James Crumbley's, Josh Horwitz, Horwitz, Karen McDonald, I'm, hadn't, Nick Suplina, Donna Bryson, Michael Perry
Organizations:
Reuters, Oxford High School, Johns Hopkins Center for Gun Violence Solutions, U.S . Department of Homeland Security, Law, Gun Safety
Locations:
Michigan, Oakland, Detroit, Longmont , Colorado