Fears were growing in Paris Saturday that a serial killer was on the loose, after the murders of four people, all by the same gun, dpa reported.
The killings have all taken place since November, with the most recent being a woman murdered on Thursday.
Police said more than 100 officers were now working on the case, news channel BFM TV reported, after all four victims were killed with the same 7.65mm gun.
However, police have so far found no link between any of the victims.
Interior Minister Claude Gueart said the authorities were working flat out on the investigation.
The victims – two men and two women – were all murdered in and around the French capital.
Prosecutor Marie-Suzanne Le Queau told a press conference that the method of attack was not idential in all four cases. In at least once case, the gunman fled on a blue-and-white motorbike.
A similar police deployment occurred in March, when self-declared Islamist Mohamed Merah killed seven people, including three children at a Jewish school, before police shot him after a siege at his apartment.