Sources say the D.A. is concerned there's no evidence placing Heather behind the wheel when her BMW hit a no parking sign on April 17 at 4 AM.
Fact is ... sources with direct knowledge tell TMZ there is no surveillance video capturing Heather's car entering her gated community immediately after the crash.
So the D.A. wants the Sheriff to spend more time and money to place Heather behind the wheel. But we're told the Sheriff's Dept. has already spent around 10 hours on the case. It will take many more hours to learn where Heather was earlier that evening and follow her tracks. One insider says it's "a total exercise in futility."
So ... with California going broke ... exactly what's on the line? The Department of Public Works for Thousand Oaks tells TMZ the sign costs $275 and there are no labor costs.
We're told this investigation will cost thousands of dollars and will ultimately go nowhere.
So, we ask ...