He enslaved, mistreated, and abused Indians who were forced to work for him. Any sign of resistance was considered hostile and tribal villages were raided and destroyed and their inhabitants murdered or kidnapped.

According to reports from travelers who visited Nueva Helvetia, Sutter enslaved many natives and forced them to work in the settlement. They were kept in inhumane conditions, imprisoned and deprived of their rights to basic hygiene. He was also convinced of rapes, not only of adult women but also of girls as young as twelve.