"The investigation proved that this group is not linked to a larger movement inside [the country] or abroad or other al-Qaida cells," Habib al-Adli was quoted by the Mena news agency as saying on Monday.
On 25 October, he had announced the arrest of five out of nine people suspected to be behind the 7 October bombings, in which 34 people were killed and 105 wounded.
Two are on the run and a Palestinian and an Egyptian attacker were killed in the explosion of one of the three booby-trapped cars parked in front of the entrance to the Hilton hotel in Taba, according to Egyptian authorities.
Al-Adli said he was convinced those held were involved in the attacks.
"The evidence is clear. The statements of reliable witnesses, materials indications all stand up and the confessions of the accused are continuing before prosecutors," he said.