An Italian prosecutor says authorities won't seek charges of illegal detention against two alleged smugglers in connection with a Mediterranean shipwreck believed to have killed more than 800 migrants.

Prosecutor Giovanni Salvi told reporters Tuesday that investigators now believe the doors to lower decks were closed to secure the boat and not to detain hundreds of migrants as prisoners. Many of the victims were believed to have perished inside the overcrowded fishermen's boat when it sank near the Libyan coast on April 18. Just 28 migrants survived and only 24 bodies were recovered.

Two alleged smugglers, including a Tunisian navigator, are being held for investigation of possible charges of causing a shipwreck, multiple counts of manslaughter and aiding and abetting illegal immigration.