Sioux Falls Police say a woman who was killed Wednesday night was in a relationship with the suspect.
Police say witnesses report 21-year-old Beverly Guerra and and 28-year-old Michael Richard Martinez were fighting earlier in the evening.
Police say later that night, Martinez used a kitchen knife to stab Guerra multiple times at their apartment on South Rock Creek Drive, which is near 26th Street and Cleveland Avenue.
Guerra's two children were in the apartment at the time; police say they were in a back room. The three and six year olds are now in protective custody.
An autopsy is taking place and police expect to know more about how many times Guerra was stabbed once that is complete.
Martinez was arrested for second-degree murder and first-degree manslaughter.
Authorities says this is the third homicide in Sioux Falls this year.