An inmate convicted of burglary escaped the van following the incident. He is currently on the run, according to officials.
At least two French prison officers were reported dead as four armed men ambushed their van on inmate transfer duty in the country's northwest on Tuesday.
The incident occurred at the Incarville toll booth near Val-de-Reuil in Normandy. The two officers, including the driver, died in the shootout, while three others were injured.
The freed inmate was being transported from the town of Rouen to Evreux. According to the domestic press, the detainee is known as 30-year-old Mohammed Amra. He is said to have been convicted of burglary and is known for cases linked to drug trafficking.
Meanwhile, French President Emmanuel Macron and Minister of Justice Éric Dupond-Moretti both expressed their condolences to the families and colleagues of the slain officers.
"Everything is being done to find the perpetrators of this crime so that justice can be done in the name of the French people," Macron said on X.
The national road R154 linking Val-de-Reuil and Artenay (near Orléans) has been closed following the incident.
The organised crime office and judicial police are currently investigating the attack.