The Beheira prosecution ordered on Sunday the detention of four men pending investigation into charges of arranging the trip for migrants on the boat that sank off the Rosetta coast late last month.
The sinking of the boat, which was on its way to Italy, resulted in the death of 202 migrants, while where 164 others survived.
At least 110 of the victims have not been identified, according the health ministry.
So far police have arrested 28 people suspected of involvement in the illegal migration scheme, including four crewmembers who survived the accident.
The suspects – all of whom are detained pending investigation – face charges including human trafficking, wrongful death, wrongful injury and using a fishing boat for another purpose.
The boat, which was carrying hundreds of migrants of different nationalities, sailed from Egypt's Mediterranean port city of Rosetta and was heading to Italy when it capsized due to overload, according to survivors.