The criminal investigation was reopened more than a year ago. If it was given to a new team, and they found evidence not found by the original team, that would be reason to then open an investigation into the original team, for doing a slipshod job.
It's still weird. Of all the things the police do routinely, RTC investigations are the most routine, verging on automated. Things like bloods, phone data, photographic and video evidence of trajectory and speed - they would all be collected before anyone had the chance to nobble the process.
Which leaves the possibility that the driver knew she had been fitting but didn't tell her doctor and carried on driving – an astonishingly stupid thing to do, if so (and I wonder how they found out, in the end).