COUNCIL BLUFFS, Iowa (AP) — Police in western Iowa have arrested a former high school math teacher accused of writing and planting notes threatening gun violence at the school.

Council Bluffs police say in a news release that 37-year-old Katrina Phelan of Council Bluffs turned herself into police on Wednesday after an arrest warrant charging her with three counts of making terroristic threats were issued for her.

Police say Phelan admitted in an interview with detectives that she had written the four notes found over two weeks in November and that she had done so to try to show that the school is not a safe place.

The school district says she is no longer employed there.