Rasual Butler Crash: Cops Retracing Steps to Find Clues

Cops have launched an investigation into the car crash that killed ex-NBA player Rasual Butler and his wife Leah LaBelle ... and they're retracing the couple's steps that night to find out exactly what went down.

We've learned investigators have visited several businesses near the crash site in Studio City, CA -- including a popular bowling alley where the couple was spotted earlier in the evening.

We know what you're thinking -- was alcohol involved? We're told cops are not specifically looking for proof Butler was boozing before the crash ... they'll know from the toxicology report.

The priority, we're told, is finding video of the couple in the car right before the crash -- in order to see what specifically caused the Range Rover to lose control and crash.

Meanwhile, we're told the autopsies on both Rasual and Leah have been completed -- and the medical examiner has said the cause is "multiple traumatic injuries" and listed the manner of death as an "accident."