An 18-year-old in Pennsylvania is accused of stabbing his girlfriend to death, and his mother is accused of helping him cover it up, according to investigators in criminal complaints against the pair.Karoline Heintz, an 18-year-old college soccer player, was found dead in the back hatch of a Jeep Cherokee, which had blood splatters inside and outside the vehicle, shortly after midnight on Aug. 20 in the borough of California, about an hour's drive from Pittsburgh, Pennsylvania State Police Trooper Rocco Gagliardi said.Her boyfriend, 18-year-old Royce Moser, has been charged with homicide and counts related to tampering with evidence, abuse of a corpse, obstruction and conspiracy. His mother, Rachel Moser, 56, was charged with hindering the apprehension of a fugitive, obstruction, abuse of a corpse and conspiracy.Authorities said in a criminal complaint that Royce Moser stabbed Heintz with a kitchen knife inside her Jeep, then dragged her into the back hatch and drove the vehicle to his mother's house. He told investigators he and his mother took steps to clean up evidence, then he drove the Jeep near Heintz's university campus while his mother drove her own car so she could drive him back home afterward, the complaint said.The stabbing happened after an argument, Gagliardi told reporters.Heintz was a freshman at Pennsylvania Western University – California, where she was a member of the women's soccer team.It was not clear if Rachel or Royce Moser had an attorney who could comment on their behalf. USA TODAY has reached out to the public defender's office for Washington County, Pennsylvania, where their charges were filed. They were denied bail on Aug. 20 and are due back in court Aug. 31, according to court records.Teen accused of killing girlfriend and covering it up with his motherHeintz and Royce Moser met up the night of Aug. 19 and were having a conversation inside the Jeep, which belonged to Heintz's family, parked outside Royce Moser's father's house in North Strabane Township, Gagliardi said. At some point the conversation went "a little bit south," he said.Royce Moser told investigators he asked Heintz to wait while he went inside the house to get something for her, the complaint said. He returned with a large knife from the kitchen and "proceeds to stab her in the chest area," Gagliardi said. Heintz fell out of the vehicle, and he dragged her to the back of the car, according to the criminal complaint.Royce Moser then drove the Jeep to his mother's house in Beallsville and they discussed what they should do, Gagliardi said. He told investigators Rachel Moser told him to bring the car inside the garage and she would help him clean it up with disinfectant spray, according to the criminal complaint."She then gave him latex gloves and told him to follow her vehicle toward the university," the complaint said.Surveillance footage obtained by investigators showed Royce Moser driving Heintz's car near the area where it was later found and wearing blue latex gloves, the complaint said. The footage showed him following another car registered to his mother, driven by a woman who was also wearing blue gloves.They drove back to Rachel Moser's house in her car, and Rachel Moser allegedly told her son to bathe and change his clothes. According to the criminal complaint, Royce Moser told investigators his mother put the knife in a trash bag and put it in the garbage outside the home and also put his clothes in the washing machine.Heintz's family called police in California to check on Heintz after an Apple Airtag in her car and her phone's location data showed she never made it back to her dorm and her father couldn't get ahold of her.Who was Karoline Heintz? Family speaks outHeintz graduated from Peters Township High School in the spring and joined the PennWest – California soccer team as a defender, according to a statement from the university's athletics department.Heintz was an "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. "Now she can no longer get to pursue her dreams."Athletic Director Dr. Karen Hjerpe said Heintz was "a bright and kind young woman with so much ahead of her."Heintz's family said in a statement released by the Pennsylvania State Police that they want justice for "our 'sweet' Karoline.""This is a parent's worst nightmare. It has been devastating for family, friends, and the whole community," the family said in the statement. "Karoline was loved by all. She was a kind, smart, beautiful girl."