The lawyer for the suspected captain of the smugglers' ship that capsized in the Mediterranean's worst migrant disaster says his client was a regular paying passenger like everyone else on board.

Lawyer Massimo Ferrante says a lot remains to be clarified about what happened when as many as 800 people drowned during the weekend crossing from Libya.

Speaking Thursday before his client was questioned by prosecutors, Ferrante acknowledged his defense is "delicate" given that survivors and even a suspected crew member identified his client, 27-year-old Mohammed Ali Malek of Tunisia, as the captain.

Prosecutors, meanwhile, are detailing their case against Malek and a suspected crewmate ahead of a hearing later Thursday to confirm their arrests.