Remember that Huma Abedin also had her devices seized as part of this investigation. Likely, the emails are on her device.
There's no way Comey would do this without external pressure - he's Clinton Foundation through and through [1]. He was brought in to clear Bill for the 140 pardons issued on his last afternoon in office (some very unsavoury folk in that - inlcuding Marc Rich) [2]. Jimmy Carter called it "disgraceful" [3]
[1] http://www.breitbart.com/2016-presidential-race/2016/09/10/e...
[2] https://en.wikipedia.org/wiki/Bill_Clinton_pardon_controvers...
[3] http://www.nytimes.com/2001/02/23/us/clinton-pardons-democra...