The truck driver who mowed down 84 people in Nice during Bastille Day celebrations appears to have been plotting his attack for months and also had accomplices, the Paris prosecutor said on Thursday.

Prosecutor Francois Molins said five suspects currently in custody are facing preliminary terrorism charges for their alleged roles in helping 31-year-old Tunisian Mohamed Lahouaiej Bouhlel in the July 14 attack.

Molins’ office, which oversees terrorism investigations, opened a judicial inquiry on Thursday.

The suspects are four men, two Franco-Tunisians, a Tunisian and an Albanian, and one woman of dual French-Albanian nationality, Molins said.

People close to Bouhlel said he had shown no signs of radicalisation until very recently. However, the French prosecutor said information from Bouhlel’s phone showed searches and photos that suggested he could have been preparing an attack as far back as 2015.

The Islamic State group has claimed responsibility for the attack, though authorities have said they had not found signs that the extremist group directed it.