Leffler, a 37-year-old former NASCAR driver, was killed during a sprint car race last week at Bridgeport Speedway in Swedesboro, N.J.
The police report concluded that a torsion stop broke off on Leffler's car. This caused part of the car's suspension to become lodged between the right-front wheel and the right steering arm, forcing the steering system to lock.
Without the ability to steer, Leffler spun 180 degrees out of Turn 4 before slamming into the outside concrete wall and overturning before the car eventually landed upright.
The report indicates that cars were averaging 135 mph and hitting speeds of 150 mph on the straightaways, though it didn't give an exact speed for Leffler's vehicle at the time of the crash.
An autopsy conducted last week determined Leffler died of blunt-force neck trauma.