A 16-year-old Indiana boy pleaded not guilty Tuesday to murder and feticide charges despite allegedly admitting to stabbing his ex-cheerleader girlfriend to death and dumping her body in a dumpster.

Charged as an adult, NBC News reported that Aaron Trejo entered his pleas during his arraignment and was ordered to be held without bail. The Mishawaka High School football player was charged as an adult for allegedly killing Breana Rouhselang, 17, a pregnant classmate who was reportedly carrying his unborn child.

Charging documents filed Monday alleged Trejo confessed to stabbing Rouhselang in the heart after an argument about her pregnancy. Trejo reportedly told detectives that he was angry with Rouhselang for waiting too long to get an abortion.

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“I took action…I took her life,” the teen allegedly said, adding that he thought about killing Rouhselang for a week before doing it.

The victim’s stepmother told reporters that Rouhselang was six months’ pregnant. The South Bend Times reported that Rouhselang was the student manager of the football team and an ex-cheerleader.

Rouhselang’s mother reported the 17-year-old missing at around midnight on Saturday. Her body was found Sunday morning in a dumpster located a block from her home.

NBC News reported that investigators questioned Trejo after the girl’s mother claimed she last saw her daughter when she went outside to have a conversation with him. Though he initially said that he planned to meet Rouhselang but she was a no-show, the report said he confessed after investigators asked if they’d been fighting about the pregnancy.

Trejo reportedly admitted to placing Rouhselang’s body in a plastic bag before placing it into a dumpster and discarding her phone and the murder weapon in the river.

An autopsy determined the pregnant teen died from multiple stab wounds and that her scarf was wrapped around her neck so tight that it’s possible she was being strangled before she died.

Trejo is due back in court on December 19.

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[Featured Image: Aaron Trejo/St. Joseph County Metro Homicide Unit; Breana Rouhselang/WNDU]