The trial of 20 men suspected of attacking a kosher supermarket outside Paris in 2012 is expected to last two months.

Two masked men threw a grenade into the Naouri grocery store in Sarcelles, north of the capital, on September 19, 2012.

The explosion was partially contained because the grenade exploded under a trolley, wounding one person. 

A fingerprint on the grenade lever led investigators to petty criminal Jeremie Louis-Sidney who had converted to radical Islamism and is believed to have been the leader of the group.

Investigators quickly discovered materials needed to make explosives in a storage space under the name of Jeremie Bailly, another petty criminal believed to have been Louis-Sidney’s right hand man.

Police found more weapons as they arrested suspects a fortnight after the incident in raids during which the alleged ring leader Louis-Sidney was killed while resisting arrest.

Other arrests were made in 2013 and 2014 as suspects were allegedly planning further attacks.

Investigators believe the group, referred to as the Cannes-Torcy Jihadist Network, was planning assaults on French soldiers, attacks on what some suspects refer to as “Zionist” targets, and some are suspected of fighting or planning to fight alongside Jihadis in Syria.

The grenade attack on the Jewish store in Sarcelles was the only attack the group effectively carried out.

Around 80 witnesses and more than a dozen experts will help determine whether the group was a network organised around Louis-Sidney or just “a group of old acquaintances, of which some have messed up” as described by one of their defence lawyers, Joseph Breham.

The trial is seen as symbolic, as the Cannes-Torcy group is suspected of being the first organised terror network planning mass attacks, a key development that may have led up to 2015’s terror attacks.