Prosecutors said Tuesday that Ahmed Ferhani had been indicted.
The charges will likely be unveiled at a June 16 court date.
Ferhani and co-defendant Mohamed Mamdouh were arraigned last week on initial charges including conspiracy as a crime of terrorism, a rarely-used state law. Both deny the allegations.
Mamdouh's lawyer agreed Tuesday to give prosecutors until June 2 to take the case against Mamdouh to a grand jury.
Prosecutors say the men were recorded discussing a synagogue attack. They say Ferhani was arrested buying guns, ammunition and an inert grenade.