Continuity mistake: When Jessica (a stunt double) rides her bicycle at the start, her red scarf is tied around her waist. A shot later, when the real Jessica is shown, the scarf hangs around her neck.
Visible crew/equipment: When Jessica gets trapped in the car, lighting equipment is reflected on the window.
Answer: In a flashback scene, it was shown that he had a violent temper, so it stands to reason that he finally killed her in a fit of rage.