A nurse was decapitated and another stabbed to death overnight in the psychiatric hospital where they worked in southwestern French town of Pau.
The head of the decapitated nurse was found on top of a television in the geriatric ward, the source said.
The second nurse had been stabbed in the neck.
"Five people are now in police custody," local prosecutor Mr Eric Maurel said. "We are investigating but we cannot say whether these persons are directly linked with the event."
Hospital workers arriving for the morning shift found the two nurses dead. There were indications that a hospital window had been forced open, Mr Maurel said.
