I'm pretty sure the ECU records a lot of stuff on it..

I'm pretty sure all SRS controllers made in the last few years have data
logging. The driving force behind it is the potential for litigation if the
airbags fire when they aren't supposed to - the devices capture the inputs
the controller uses for its decisions on a continuing basis, overwriting the
oldest data. I don't know the typical recording time window, but I suspect a
large part of a minute before the airbags deploy is captured. More would be
unnecessarily expensive, and much less would not document the correctness of
the decision very well.

The recorded data certainly includes speed, and probably at least forward
acceleration/deceleration. In the case of side curtains, there is probably
also lateral acceleration recording.

Mike