| Mohamed Lahouaiej-Bouhlel was shot dead after ramming his lorry into crowds |
The Tunisian man who drove his lorry
into crowds of people in Nice researched the route in the days before
the attack, French media have reported.
Six people are being held in connection with the killings.
The latest, an Albanian couple who have not been identified, were arrested on Sunday morning, French judicial sources said.
Lahouaiej-Bouhlel was shot dead by police when his vehicle's path along the Promenade des Anglais was eventually halted. Europe 1 radio said CCTV footage from the days beforehand showed him driving through the area in the lorry, closely observing the scene.
On the day itself, Lahouaiej-Bouhlel phoned his brother in Tunisia during the afternoon, sending a photograph of himself among the crowds, Reuters news agency reported.
"That last day he said he was in Nice with his European friends to celebrate the national holiday," the brother, Jabeur, said, adding that in the photo "he seemed very happy and pleased, he was laughing a lot".