BLACKMAN TOWNSHIP, Mich. (AP) — Authorities say a 13-year-old boy has been taken into custody after threatening violence at a school district in southern Michigan.

Jackson County Undersheriff Chris Kuhl tells the Jackson Citizen Patriot that the former student from Blackman Township made the threat Thursday against East Jackson Community Schools. Police got involved after the threat on social media was reported by other students.

Superintendent Steve Doerr says classes were taking place Friday with an extra law enforcement presence inside and outside of buildings.

Authorities interviewed the boy and Kuhl says they determined it was “an ill-conceived joke.” He says no weapons were found.

There have been numerous threats in Michigan and other states since 17 people were killed last month at Marjory Stoneman Douglas High School in Parkland, Florida.