(CNN) A 16-year-old Indiana high school football player confessed to fatally stabbing a pregnant schoolmate after she waited too long to tell him about the pregnancy to get an abortion, according to court papers.

Aaron Trejo, a member of the Mishawaka High School football team, was charged Monday with murder and feticide in the death of Breana Rouhselang on Saturday. The 17-year-old junior and cheerleader at the school east of South Bend was six months pregnant, her mother told police, according to an affidavit. An autopsy confirmed the pregnancy.

Trejo entered a preliminary plea of not guilty at his arraignment on Tuesday and will be held without bond. His next court date is December 19.

Trejo told authorities he was aware of Breana's pregnancy and that he was alleged to be the father, the affidavit said, but he said neither wanted to have the baby. He said the two fought about the child before he stabbed Breana in the heart with a knife on Saturday, according to the affidavit. He then put a black plastic bag over her, put her body in a dumpster, and threw her phone and the knife in a river, court papers said.

"I took action ... I took her life," he said, when asked by authorities what he did when he learned she had waited too long to get an abortion by the time she told him of the pregnancy, according to the affidavit.

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