Only the actual district attorney is elected, and the DA is seldom responsible for the actual trying of cases. The DA is usually pretty far removed from the minutia of actual casework.
Social network analysis using known tampered cases should be enough to highlight all the DAs that could require further scrutiny. I would not be surprised if SNA shows that a few DAs in particular show up over and over and over again in these tampered cases. AFAIK, the DAs are the civil servants with the most to gain and lose from conviction rates and therefore are the most likely to have been involved, assuming others collaborated or were at least complicit.
