An Egyptian public prosecutor ordered on Tuesday that the cases of police officers accused of killing 37 detained Morsi loyalists be sent to the criminal court.
On 18 August, the Interior Ministry confirmed 37 Morsi supporters had died of asphyxiation due to teargas and overcrowding while they were being transferred to Abu Zabaal prison in Cairo.
Security forces claimed the prisoners had died during an escape attempt. However, prosecution investigators said this was not true.
The accused officers were detained on Tuesday for four days pending investigations.
Egyptian police have long been accused of using excessive force and torture. The January 2011 uprising, which led to the ouster of Hosni Mubarak, started as a protest against police brutality.