We do know that the board of directors of the Second Mile includes many wealthy and powerful people. If the whole truth came out, they could be sued for millions. So there were a lot of people who had an interest in covering up.
Incidentally, if some of those people were willing to snuff out a DA and make his body disappear (which seems possible), it would be easy for them to get into the DA's home and plant those searches about "cleansing" hard drives. Covert breakins are child's play to rich people and the PIs they can afford to hire. I speak from experience.