The boat was carrying 55 people along the Musi river when it was hit by a large wave and sank amid bad weather on January 3, South Sumatra water police chief Robinson Siregar said.
He said the police were still searching for the captain. Meanwhile, his assistant has been detained for questioning to find out whether or not the boat was seaworthy or there was negligence by the crew.
It was the latest deadly maritime accident in the Indonesian archipelago, which relies heavily on boats to ferry people around its 17,000 islands.
On New Year's Day, at least nine people died after a passenger boat capsized when traveling from the city of Tarakan to Tanjung Selor on Borneo island. Vietnamplus