MELVINDALE, Mich. (AP) — A 12-year-old boy is accused of making a threat that led to three days of no classes in a Detroit-area school district.

The Wayne County prosecutor’s office says the minor appeared Thursday in Juvenile Court. Schools in the Melvindale-Northern Allen Park district opened Thursday for the first time this week.

Police say the boy made a threat toward students at Strong Middle School through a phone app Sunday. Superintendent Kim Sorrano says police discovered a new social media post during the investigation, but it didn’t turn out to be a new threat.

In a letter to the community, Sorrano told parents that a police officer would be assigned to schools in the Melvindale portion of the district.