Italian authorities on Thursday released more details of abuse and violence described by survivors of a migrant ship that sank in the Mediterranean, including the killing of a young man who stood up without the permission of smugglers, The Wall Street Journal reported.

At least 850 migrants died after a merchant ship that was diverted to rescue them collided with the decrepit fishing boat. It sank so quickly that hundreds of people crammed into the lower decks had no chance to escape.

Prosecutors in the Sicilian town of Catania who are handling a criminal investigation reiterated that the boat toppled when the captain collided with the rescue boat three times.

According to one migrant, prosecutors said, a young man was killed by smugglers because he stood up without permission on the rubber raft that was bringing them from the Libyan coast to the fishing boat.

His dead body was thrown in the water, prosecutors say the migrant reported.

According to other survivors’ accounts, between a thousand and 1,200 migrants were kept for more than a month at a farm near Tripoli where they were repeatedly beaten with wooden sticks if they did not follow the smugglers’ orders.