Habib Al-Adly said the shadowy, Gaza-based Army of Islam in Gaza was behind the attack, which sparked three days of Christian rioting in Cairo and several other cities. It was the deadliest attack against Christians in Egypt in more than a decade.

Security officials said an unspecified number of people have been detained in connection with the bombing but gave no more details. They spoke on condition of anonymity because they were not authorized to share the information with the media.

The Army of Islam is thought to have participated in the kidnappings of Israeli soldier Sgt. Gilad Schalit in 2006 and BBC journalist Alan Johnston, who was later released.

Late last year, Israel killed three members of the Army of Islam in separate airstrikes, alleging the men had planned to attack Israeli and American targets in Egypt’s Sinai Peninsula.