An Italian nurse murdered patients "for pleasure" and enjoyed "the challenge", it has been claimed.
Daniela Poggiali, 41, also took photographs of herself with dead patients.
She was arrested by police in Lugo, Italy, following the unexpected death of a patient who was admitted with a routine illness, the Mail online reported. The probe was later widened to include 38 deaths.
Poggiali allegedly targeted patients she thought were annoying or who were visited by 'pushy relatives.'
"We believe she is sound of mind, but simply took satisfaction, and real pleasure in killing", Alessandro Mancini, the magistrate leading the inquiry, said.
Police started the probe after the death of Rosa Calderoni, 78, in April, who was recovering from a broken femur and was admitted to the hospital feeling dizzy.
During a post-mortem doctors found high traces of potassium chloride. It was also found in a drip investigators believe the nurse was using.
Potassium can stop the heart and is one of the components used in the lethal injection given to death row inmates in the US.