The man who plowed a truck into a crowd during Bastille Day celebrations in the Riviera city of Nice last week – killing at least 84 and injuring hundreds – plotted his attack for months and had accomplices, the Paris prosecutor announced Thursday.

Speaking to reporters in the capital, François Molinssaid an analysis of the attacker’s cellphone revealed both photographs and search histories suggesting that Mohamed Lahouaiej Bouhlel, the 31-year-old Tunisian-born man who drove the truck, had contemplated an attack as early as 2015.

Molins also confirmed that five suspects have been taken into custody and will face preliminary terrorism charges for their alleged roles in the July 14 attack.

A previous announcement by the prosecutor’s office revealed that Bouhlel had sought information online about other similar attacks, such as the recent shooting at an Orlando nightclub and the killing of Dallas police officers.

His computer was said to have contained pictures of Osama bin Laden, coverage of the attack on the editorial offices of the satirical publication Charlie Hebdo in January 2015, and what Molins earlier this week described as “pictures of corpses and pictures related to radical Islam.”

In the aftermath of the Nice attack, the Islamic State declared Bouhlel a “soldier” of the militant group’s self-proclaimed caliphate, although French authorities said their investigation has not found any direct links between Bouhlel and the Islamic State.

(c) 2016, The Washington Post · James McAuley