The police should list "lack of skill" as a cause, not speed.
The National Transportation Safety Board's aircraft accident investigations are an excellent model for this. The vast majority of aircraft accidents are caused, ultimately, by "pilot error", analogous to "lack of skill". I'm guessing the police don't have a year to spend investigating each and every accident, though. (That's the typical time period of an NTSB investigation, and obviously the NTSB has several orders of magnitude fewer accidents to investigate each year.)