ROME — Italian officials said on Tuesday that they had arrested the captain and crew of a boat in which 49 migrants suffocated over the weekend after they were blocked from leaving the ship’s hold.

The eight men, who said they were from Libya, Morocco and Syria, are accused of multiple homicide and illegal immigration, officials said at a news conference in Catania, Sicily, where the Norwegian ship that transported the 312 survivors of Saturday’s rescue remains docked.

The boat’s other passengers identified the crew members during questioning with rescuers and officials, in which they described a nightmarish crossing.

Survivors said that the crew had maintained order on board by “preventing people from emerging from the hold, where the air was unbreathable because there were so many people down there, along with the gas fumes from the ship’s motors,” the Catania prosecutor, Michelangelo Patanè, said at the news conference.