(CBS Detroit) -- More than 100 schools have closed across Michigan following the shooting at Oxford High School and copycat threats.
About 80 of those schools are in the Metro Detroit area.
Many schools are expected to close on Monday, and parents are urged to check their student's school website.
However, most schools will return on Monday with extra patrol across campuses.
Ethan Crumbley, 15, who is who is accused of firing multiple shots in Oxford High on Nov. 30, has been charged as an adult with two dozen crimes, including murder, attempted murder and terrorism. Four people -- all students -- were killed and seven others, including a teacher, were injured.
Oakland County Prosecutor Karen McDonald filed involuntary manslaughter charges Friday against the teen's parents. Authorities said a search is underway to locate the Crumbleys, but two attorneys who say they are representing the couple released a statement saying the couple had left town for their safety and are returning for an arraignment.
Oakland County Sheriff Mike Bouchard said no threats in the county were found to be credible.
On Thursday, the Southfield Regional Academic Academy Campus canceled classes after a student brought a gun to school Wednesday.
"If you're making threats, we're going to find you," Bouchard said. "It is ridiculous you're inflaming the fears of parents, teachers in the community in the midst of a real tragedy."
In Macomb County, officials said deputies were making extra patrols at all schools this week after receiving 28 calls for reports of school threats within the first few days after the shooting.
"School shootings are one of our biggest fears as a student, a parent, school staff, and law enforcement," the sheriff's office said in a statement.
In Genesee County, a Flint teenager was charged with making a false threat when she recorded a video while riding a school bus and posted it online.
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