Oxford Community Schools announced it closed its middle and elementary schools on Tuesday over a “specific threat” made on social media. Students will return on Wednesday after law enforcement swept the buildings, the district said on its website. Oxford High School, where Ethan Crumbley allegedly killed four students and injured seven in a mass shooting two weeks ago, remains closed.

Following the Nov. 30 mass shooting, “dozens of threats have been made all across Oakland County in multiple school districts,” a county undersheriff told ABC News on Tuesday. “It is out of control.” Wayne County prosecutor Kym Worthy said last week that she had issued charges against 23 underage suspects for making threats of violence, with another 10 investigations ongoing. The youngest charged is 9 years old.