It's possible to dig the airbag controller out of the wreckage and read out the last 30 seconds or so. Airbag controllers have a short but nonvolatile memory and usually survive crashes. That gets you speed, acceleration in several axes, plus steering, brake, and power inputs, and detailed info about what the airbag system did.[1] Those were originally created to tune the airbag algorithm, and, over the years, false airbag deployments have dropped almost to zero.
That's the basic info needed to analyze fatal crashes. Speed at collision? Speed 10 secs before collision? Accelerator and brake inputs? Maneuvering (side accel) before crash? That, plus the crash scene, tells most of what you need to know.
Law enforcement will sometimes read out those units, when it's not clear what happened. It's not done routinely.
[1] https://www.nhtsa.gov/sites/nhtsa.gov/files/fmvss/EDR_QAs_11...