FARGO (AP) - Fargo police say an investigation into a crash that killed an 8-year-old girl and injured her sister will take a few more days.

Police Sgt. Jeff Skuza says officers took skid tests on Wednesday, the day of the crash, so they could consider road conditions that were "fairly nasty" at the time.

Skuza said officers also plan to look at vehicles and digitally map the scene.

Mayor Dennis Walaker says there is "no question" a rut on the city's University Drive South caused the crash. The city has hired a private investigator to check when city workers were notified of the problem.

Eight-year-old Amanda Leininger of Fargo died of injuries in the three-vehicle crash. She was in a car driven by her 15-year-old sister, Jessica, who was released from the hospital Thursday. People in the other two vehicles, a minivan and a sport utility vehicle, were not hurt.