IndyCar officials have said that British driver Dan Wheldon was killed after he collided with a fence pole.
The 33-year-old died following a 15-car crash at the Las Vegas Motor Speedway track on October 16.
The organisation, who took two months to conclude their investigation, said that the pole "intruded in the cockpit and made contact with the driver's helmet and head".
Questions had been raised after the incident over the safety of 34 cars going around the track.
However, IndyCar said that the number of cars on the circuit was "deemed to be acceptable".
