They might also be looking for emails with the unmarked classified info they found in Hillary's emails, that pre-date those emails and are marked as being classified. That will belie Hillary's claims that any classified information she sent wasn't marked as classified until after the fact.
Whoever knew to jump the air gap knew to strip the markings.
This will tell them who sent what to whom and when.
Funny thing about government scanners... most are network jobs that email you the document. If someone scanned the marked version and used Adobe to strip it, that info will be found.
Someone somewhere has a lawyer on speed dial.