Mohamed Lahouaiej-Bouhlel, the man who drove a truck into a crowd on the promenade in Nice on Bastille Day, killing 84 people, plotted his attack for months and had accomplices, the Paris prosecutor has said.

Francois Molins said his office, which oversees terrorism investigations, said five suspects currently in custody are facing preliminary terrorism charges for their alleged roles in helping Bouhlel.

Molins said information from Bouhlel’s phone showed searches and photos that indicated he had been studying an attack since 2015.

The new details came as French government tried to reassure its citizens following the country’s third major attack in 18 months.