Egypt's general-prosecution ordered on Tuesday the detention of Sinai militant Adel Habara, and two others, for 15 days, pending investigations into their alleged involvement in the killing of 25 Central Security Forces conscripts in August.
Habara, a wanted militant in Egypt's restive Sinai Peninsula, was arrested on Saturday. The following day, a security source told state news agency MENA that he had confessed to the murder of the conscripts.
The 25 conscripts were reportedly stopped on their way back to the barracks near Al-Arish city in northern Sinai on 19 August, when they were allegedly lined up and shot in one of the worst militant attacks on security forces in the peninsula in recent months.
Two other detainees face charges for attacking military and police sites in northern Sinai.
Habara has already been sentenced to death in absentia on charges of involvement in the bomb blasts of Taba in 2004 and Dahab in 2006, both touristic sites in Sinai, which left 42 dead.
The Egyptian Army and police have been engaged in an operation against militants in North Sinai, which borders the Gaza Strip and Israel.
Since the ouster of Islamist president Mohamed Morsi on 3 July by Egypt's armed forces following mass protests, militants have staged repeated attacks on military and police sites, killing dozens of forces.