Updated

Prosecutors in Sicily detained 10 people on suspicion of smuggling and murder Friday for having allegedly crammed dozens of migrants into the airless hold of a boat where 52 bodies were found this week.

The Swedish ship Poseidon rescued 439 survivors Wednesday but crew members made a grisly discovery when they looked into the hold. The rescuers ended up smashing the deck to reach the 52 corpses inside.

Carmine Mosca, head of the Palermo police squad, said Friday that survivors who came ashore late Thursday told authorities how the smugglers would beat the migrants back with knives if they tried to come out of the hold for air.

"When theses migrants tried to relay their need for air and water, they were mishandled, injured, knifed in a truly fierce way," Mosca said.

Palermo prosecutor Maurizio Scalia said the detained crew included seven Moroccans, two Syrians and a Libyan who was the "violent" enforcer of order on the ship. The migrants hailed mostly from sub-Saharan Africa: Sudan, Senegal, Nigeria but also Pakistan and Bangladesh.

Officials believe the cause of death was likely asphyxiation: Scalia said the hold of the 20-meter boat contained about 60 people, was only about a meter (three feet) high, with two small windows and the boat's engine.

He said murder charges, rather than manslaughter, were warranted since the smugglers "eventually accepted the risk that these people, in these conditions, could die."

In previous crossings, the smugglers would charge an extra 4,000 euros ($4,520) apiece for places above deck and an additional fee if they wanted life jackets. However, that distinction wasn't used in this operation, Mosca said.

The crew leader simply directed the migrants above or below deck as they boarded, regardless of what they had paid, Mosca said.

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AP producer Fabio Platania in Palermo contributed.