West Alexandria prosecution services released late on Sunday Major Adham al-Rouby, a former agent of the disbanded State Security Investigation Services (SSIS), after interrogations over his alleged involvement in torturing a young Salafi preacher to death.
The family of Sayed Belal, 31, accuse security authorities of torturing Belal to death during interrogations at a police station in January.
Police authorities had said Belal was involved in the bombing of an Alexandria church on New Year's Eve, which killed 23 and injured dozens.
State-run news agency MENA said Rouby proved he was on vacation at the time of the incident.
Other suspects in the case include Major Mohamed al-Shimy, an officer at the National Security Authority's bureau in Marsa Matrouh and a former SSIS agent in Alexandria, where he handled Salafi activities. He used the pseudonym Alaa Zeidan while interrogating suspects.
On Sunday, prosecutors extended Shimy's detention period for 15 more days pending investigations.