France murders: Two suspects held in Paris suburb
The first victim was killed in November and the fourth - a 48-year-old mother - was shot dead on 5 April.
Prosecutors say the same semi-automatic gun was used in all four attacks in the Essonne district, but police have not yet found it, BBC News reports.
A motorbike has been seized, similar to one described by witnesses.
One of the suspects, aged 33, was detained as he left his parents' home in the Paris suburb of Ris-Orangis.
Police have ruled out a connection with last month's killings around Toulouse, but no motive for the latest shootings has been determined.
In Toulouse a self-professed Islamist militant, Mohamed Merah, was shot dead by police, following attacks in which he murdered seven people, including three children.
In the Essonne killings the gunman fled on a motorbike each time, like in the Merah case.
The seized motorbike was found less than a kilometre from the latest murder scene in Essonne, Le Parisien news website reports.
Extensive searches were carried out after the first arrest on Saturday.
The fourth victim was a widow and mother of Algerian origin, shot in the foyer of her apartment block in the Grande-Borne area of Grigny, which is adjacent to Ris-Orangis.
The killing followed three others:
- 27 November: Laboratory assistant, 35, in Grigny
- 22 February: Man, 52, neighbour of first victim, also in Grigny
- 19 March: Man, 81, shot in Ris-Orangis
A man turned himself in for the first killing, but then retracted his confession and the other killings took place while he was in custody.
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