A nurse in Italy is accused of killing 38 patients because she thought they were “annoying.”

Daniela Poggiali was arrested Friday on murder charges, Italian newspaper Corriere di Bologna reports. The 42-year-old nurse caught the attention of authorities after the April death of 78-year-old Rosa Calderoni, according to the Independent’s translation of Italian newspaper Libero Quotidiano.

Calderoni was admitted to a hospital in the town of Lugo with a diabetes-related ailment, and died from what officials believe was a fatal injection of potassium chloride. Prosecutors say that their investigation is more difficult because potassium chloride fades from the bloodstream within a couple days, making it hard to detect.

Calderoni’s death occurred while Poggiali was on duty, and the resulting investigation found that 37 other patients also died mysteriously on her watch. Authorities now suspect that Poggiali may have killed them all because she thought that they or their families were irritating.