Fresh information about last week's deadly truck attack in the French city of Nice shows the attack had been planned for months and the attacker had accomplices.
Mohamed Lahouaiej-Bouhlel drove a truck into a crowd celebrating Bastille Day on a seaside promenade, killing 84 people.
The Islamic State militant group claimed responsibility for the attack and five suspects with links to Lahouaiej-Bouhlel have appeared in court.
Paris prosecutor Francois Molins said phone records showed Lahouaiej-Bouhlel was in regular contact with several conspirators.
"At this stage of the investigation and based on various photographs it appears that Mohamed Bouhlel had premeditated his criminal attacks several months before the 14th of July," his translated words said.
Among evidence revealed by the prosecutor were photographs of the Nice promenade on Bastille Day the year before the attack, in 2015.
Those facing terrorism charges over the attack included four men and one woman, aged between 22 and 40.
An Albanian couple suspected of providing Lahouaiej-Bouhlel with a pistol were among them.
A 22-year-old man was believed to have received text messages from Lahouaiej-Bouhlel on the night of the attack, discussing the supply of weapons.
Like Lahouaiej-Bouhlel, none of those detained were known to French intelligence prior to the attack.
His estranged wife was initially among those arrested but she was later released.