Bruce Jenner -- Cops Just Scored Critical Crash Video

A video has surfaced of the fatal car accident involving Bruce Jenner -- a video taken seconds after impact -- and we've learned it could become a critical piece of evidence for law enforcement investigating the accident.

Law enforcement sources tell TMZ ... the L.A. County Sheriff's Dept. just obtained the video, which shows the immediate aftermath of the crash. Most important, it shows people who witnessed the chain of events that led to the Lexus Bruce hit veering into oncoming traffic and killing the driver.

We're told Sheriff's detectives are on the hunt for the people in the video because, among other things, they might have seen the Prius that was hit by the Lexus. Cops want to know if the Prius was stopped behind a long line of cars waiting for the light to turn green, or whether it illegally stopped for some other purpose.

We're told the actions of the Prius and Lexus drivers could have a significant impact on Bruce's culpability for the fatal crash.

And we're told the video shows Bruce was NOT being chased by paparazzi ... something Jenner family sources told us the day of the crash.