A Pennsylvania college soccer star was stabbed to death by her boyfriend — who claimed “demons” told him to harm her — as the suspected murderer had help from his mother in disposing of his partner’s body, according to police.

Karoline Heintz was found dead in the back hatch of her Jeep Cherokee at around 12:30 a.m. Thursday, just outside the Pennsylvania Western University campus in California, Pa.

Heintz, an incoming freshman on the university’s women’s soccer team, had met up with her boyfriend, Royce Mosher, after she attended a family party earlier in the evening, Pennsylvania State Trooper Rocco Gagliardi told reporters.

The couple got together at Mosher’s father’s home in North Strabane Township, where they began talking about their relationship inside her car before the discussion turned a “little bit south.”

“They’re a younger couple talking about how relationships can continue maybe in a college setting. Somewhere that conversation probably goes a little bit south,” Gagliardi said. “Towards the end of that conversation between boyfriend and girlfriend, he goes inside and grabs a large knife from the kitchen.”

The teen allegedly told Heintz he had something for her, which allowed him to run inside and grab the weapon.

Mosher returned to the vehicle, where he was accused of stabbing Heintz in the chest as she fell out of the car.

Mosher allegedly stuffed his girlfriend in the back hatch of the Jeep before racing to his mother’s home in Beallsville, Pa., looking for help.

“They tried to clean clothes, tried to clean the car up, tried to get rid of any blood stains possible and then proceeded to take that vehicle with the mother tailing all the way down to California Borough,” Gagliardi said.

Heintz’s family called police for a wellness check on the teen after she failed to check in with them when she was supposed to have returned to her dorm room.

The teen’s location pinged outside the California Borough Library, where officers found her body in the back of the abandoned, blood-stained car, Gagliardi said.

Mosher and his mother, Rachel Mosher, were arrested Thursday morning.

The teen allegedly confided in his mother that he had a “demon take over” and was told to stab Heintz, CBS News Pittsburgh reported.

Officials did not reveal a motive behind the stabbing and didn’t say if mental history played a factor in Mosher’s alleged attack.

“It is more of an unfortunate event, 18-year-old girl, young soccer star ready to explore life, ready to start college, now can no longer get to do that,” Gagliardi said.

Mosher was charged with criminal homicide, two counts of tampering with evidence, two counts of abuse of a corpse and obstruction.

He remained stone-faced as he was led out of a police station Thursday evening, handcuffed and wearing a white prison jumpsuit.

His 57-year-old mother was charged with tampering, obstruction, hindering the apprehension of a fugitive and abuse of a corpse.

She hid her face and kept her head down as she was hounded by reporters during her walk out to a police car.

The elder Mosher claimed she “did not” do it before apologizing to Heintz’s family, according to video from WTAE.

“I’m sorry,” Rachel Moser said as she climbed into the car. “That my son took a life.”

Heintz had graduated from Peters Township High School in June.

She was set to start her collegiate career at PennWest University, where she had committed to play Division II soccer, with the team’s first game set for Aug. 29.

“PennWest University is deeply saddened by the tragic death of Karoline Heintz, who was a first-year student at the California campus. Our heartfelt condolences go out to her family, friends, and all those affected by this tragedy,” the school said in a statement.