A fourth person has died after Tuesday's attack on a Christmas market in Strasbourg, prosecutors said.
The Paris prosecutor's office did not reveal the identity of the fourth person who died but said the victim was among those injured in the shooting and was previously described as "in critical condition".
It came as investigators try to establish whether the main suspect was helped by accomplices while on the run.
Paris prosecutor Remy Heitz, who handles terror cases throughout France, told a news conference that seven people are in police custody, including four members of Cherif Chekatt's family.
The 29-year-old was shot dead on Thursday during a police operation in the Neudorf neighbourhood of the city.
"We want to reconstruct the past 48 hours in order to find out whether he got some support," Mr Heitz said.
After a two-day manhunt, Mr Heitz said, on Thursday evening three officers patrolling in Neudorf spotted a man corresponding to the suspect's description.
He noticed their vehicle and tried unsuccessfully to enter a building. When police officers identified themselves, Chekatt turned around and opened fire.
"A projectile hit the vehicle above the left rear door, two police officers responded, shooting several times, and killed him," Mr Heitz said.
Investigators found a gun, a knife and ammunition on Chekatt's body.