The Tunisian who rammed a truck into Bastille Day crowds in Nice, killing 84 people, sent a text message just before the attack about the supply of weapons, a source close to the investigation said Sunday.
In the message, 31-year-old Mohamed Lahouaiej-Bouhlel "expresses satisfaction at having obtained a 7.65mm pistol and discusses the supply of other weapons", the source said.
The driver, who was shot dead by police after his deadly rampage, took pictures of himself at the wheel that he shared by SMS, the source added.
Over 200 investigators are working on identifying the recipients of the messages, one of the officers told AFP.
Six people are still being held for questioning over the third major attack in France since January 2015.
Among the six is a 38-year-old Albanian, who was arrested on Sunday morning on suspicion of supplying the pistol that Lahouaiej-Bouhlel used to fire at police trying to block his route.
Police later found the gun in the truck, along with two replica assault rifles and a dummy grenade.
Lahouaiej-Bouhlel's estranged wife was released on Sunday after two days of questioning.