Clinton Staffer who ‘Retrieved’ Private Server Emails refused to appear on Select Committee 

Hillary’s Email Server Technician during her 2008 campaign chose to plead the 5th Amendment rather than testify during her trial and later refused to appear on a Select Commitee despite being Subpoenaed.
In the latest WikiLeaks publication of the Podesta emails, a Clinton staffer questions the events that took place:

Neera Tanden email to John Podesta, Sep 3rd 2015