What does Huck discover on the steamboat? CH 12-16

Huck convinces Jim to tie the raft to the boat and climb on board. They are surprised to hear voices, which Huck goes to investigate. There are three robbers on board, two of whom have tied up the third man. Apparently the bound man had threatened to turn them all in to the state. One of the robbers wants to kill him immediately, but the other man restrains him. The two men finally decide to kill their partner by leaving him on the boat and waiting until it sinks.