Jennifer Syme, 29, a record-industry worker who was the girlfriend of "The Matrix" star Keanu Reeves and the mother of the couple's stillborn baby girl last year, was killed in a car accident that took place in Los Angeles early Monday morning, police authorities have told PEOPLE. "For unknown reasons, she collided into three parked vehicles," said LAPD spokesman Hayley Prece. "She was instantly killed. It is currently unknown if alcohol or drugs were a factor in the collision." On Wednesday the L.A. coroner began conducting an autopsy and tests for drug and alcohol, said a spokesman for that office, who added: "Keanu called our office and confirmed her identity on Tuesday and that they were still together. Her mother also confirmed that fact to us." Syme was a former assistant to filmmaker David Lynch ("Blue Velvet") and to controversial rocker Marilyn Manson. She reportedly met Reeves, 36, through record industry friends at a party where Reeves was promoting his rock band, Dogstar.