Egyptian Justice Department decided on Monday to detain Alaa Mubarak, the eldest son of former president Hosni Mubarak for another 15 days under investigations over charges of illegal gains, state news agency MENA reported.

Assem el-Gohary, Assistant Justice Minister for illicit gains authority (IGA), said Alaa was charged of joining his father and younger brother Gamal Mubarak to grab illegal wealth, as well as partnership with former chief of the stock market for gaining illicit financial interests.

Investigations with Alaa and Gamal began on Monday by the IGA, and a team of IGA investigators arrived at the Torah prison in Cairo for the questioning session of the two brothers, according to MENA.

Meanwhile el-Gohary ordered to reveal secrets accounts of Alaa and Gamal after they signed a statement in English, French and Arabic to disclose their accounts in and outside Egypt.

Mubarak and his two sons were ordered on April 13 to be put under custody, facing charges of killing protestors and embezzlement of public funds among others.

Egypt's General Prosecutor Abdel Maguid Mahmoud decided last week to refer Mubarak and his two sons to the criminal court over charges of intentionally killing peaceful protesters.

Mubarak was forced to resign on Feb. 11 after 18 days of mass protests against his 30-year-long rule. He is now under custody in a hospital in the Red Sea resort Sharm El-Sheikh.