SIOUX CITY, Iowa (AP) — An 18-year-old in northwestern Iowa has pleaded not guilty to charges that he stabbed to death his ex-girlfriend and another young man.

Court records say written pleas were filed Tuesday in Woodbury County District Court for Tran Walker, who's charged with two counts of first-degree murder. The records don't show that a trial date has been set.

He's accused of killing 17-year-old Paiten Sullivan and 18-year-old Felipe Negron Jr., who both lived in Sioux City. Police say Walker was in a car with the other two on Jan. 28 when he began to stab Sullivan because he was upset that she had broken up with him. Police say that when Negron tried to intervene, Walker stabbed him, too.