Cheryl Mills, who served as Hillary Clinton's chief of staff while she was secretary of state, knows more about the reasons behind the Democratic front-runner's secret email server than she's willing to say, Judicial Watch President Tom Fitton said Wednesday."I think she knows more than she's willing to say in the sense that we asked questions specifically on that," Fitton told Fox News' "Fox and Friends" program, on the day after Mills' deposition testimony was released by Judicial Watch, a conservative watchdog group. "We were told we couldn't get into it for attorney/client [privilege] and other reasons."For example, Fitton said, Mills talked with Bryan Pagliano, the State Department employee who had set up Clinton's personal email server."He supposedly asserted his Fifth Amendment [rights] and he has immunity, [so] we wanted to know, what did they talk about, what did she learn?" said Fitton. Mills testified that she was speaking with Pagliano as Clinton's attorney, said Fitton, "so you can't find out."Fitton said Mills arrived with seven attorneys, including herself, while Judicial Watch had four, and he attended the deposition as president of Judicial Watch."It was tough going for the attorney who was conducting the questioning, because the government lawyers and Mrs. Mills' personal attorney objected vociferously to many of the questions," Fitton told Fox News.Fitton said Judicial Watch wanted to find out about Clinton's email system and how the system "impacted the Freedom of Information Act, the American people's right to know...Ms. Mills admitted that FOIA was impacted negatively and she suggested that they wish they had thought of that at that time."Moving forward, Fitton said Judicial Watch wants to know where Clinton's missing emails went."Mrs. Clinton only turned over half the e-mails she took with her," said Fitton.Pagliano will be deposed next week as well, said Fitton.