Hillary had a huge problem. In order to PROPERLY delete some of her emails she would have to bring in an IT specialist or some such which would also place her damning emails at risk of being acquired by said person. So, she kept it in-house and had one of her side kicks (can't remember his name) do it but he didn't 'wipe' properly.
Bringing in a specialist would require that she kill him after he was done. She didn't want to risk it this time.