A Tunisian boat captain has been arrested and charged with manslaughter after a boat carrying 850 migrants capsized Saturday in the Mediterranean Sea just north of Libya, drowning most of the passengers.

This could be the deadliest known disaster involving migrants crossing the Mediterranean from North Africa, CNN reported.

Most migrants who try to leave Africa on fishing boats bound for Europe originate from Eritrea, Somalia, and Nigeria, according to CNN. They also come from Gambia, Senegal, Mali, Sudan and Cote d’Ivoire.

Mohammed Ali Malek, 27, was arrested along with a Syrian crew member on suspicion of “reckless shipwreck, multiple manslaughter (and) abetting clandestine immigration” in the disaster, CNN reports.

Just 28 people were rescued in all — 22 by the Phillipine crew aboard the King Jacob, a cargo ship that went to the aid of the migrant boat, according to CNN. About 24 bodies had been recovered as of Monday, leading authorities to believe that most of the victims sank with the boat.

Most of the survivors were men in their 20s and 30s including one man from The Gambia, the lone survivor in a group of about 80 Gambians.

Several scenarios are being considered as to how the boat sank. One is that Malek may have caused the boat to sink when he caused it to collide with the merchant ship that had come to help, according to the Catania office, which is headed by prosecutor Giovanni Salvi, CNN reports.

Another is that the migrant ship tipped over after everyone ran to one side of it. A third is that the 20-meter (66-foot) boat was simply overcrowded, with about 850 people on board. A Bangladeshi survivor told authorities that smugglers had locked many people inside the lower decks.

The Italian Navy rescued more than 80,000 people in the Mediterranean Sea in 2014, according to CNN. Commercial ships rescued more than 40,000 people, according to the International Organization for Migration. More than 35,000 people were rescued by the Italian coast guard.