An Italian nurse has been arrested this week on suspicion of killing up to 38 patients because she found them irritating. Daniela Poggiali (42) is also reported to have taken photographs with the patients' dead bodies. The nurse, who was based at a hospital in Lugo in northern Italy,  is believed to have killed patients when she felt that their relatives or they themselves were too pushy. Poggiali originally came under suspicion following the death of 78-year-old Rosa Calderoni when it was discovered that the elderly woman had been killed by a potassium chloride injection.  This death prompted an investigation which then implicated Poggiali in 38 other mysterious deaths. According to Italian newspaper Corriere Della Sera, chief prosecutor Alessandro Mancini told a press conference that the police had found a selfie on Poggiali’s phone which shows her giving a thumbs-up in front of the deceased patient. He also added that she was “unperturbed” when arrested. Colleagues of Poggiali have since spoken out about her, with one adding that they suspected her of giving laxatives to patients. There are many difficulties facing the investigation, with the main one being the fact that potassium fades from the bloodstream within a few days, thus making it hard to detect.