Evidence the state department knew she is innocent was furnished by Charlie. He is the only person I know to have stated this. He claims this, because he and others presented irrefutable evidence. Hell, I knew she was innocent as soon as I joined JREF, they were all explaining it two years ago, without challenge except mainly Machiavelli. I had read both the Massei report and the Hellmann report. The first was ridiculous, the second was complete and foolproof.
So going into March 2015, the series is two one to the dolts, Massei and Nencini, against Hellmann.
Remember also that Hellmann publicly stated he had been ostracised by his colleagues and forced to retire. The line of least resistance is to convict.
Now, the State Department can do nothing or do something. Remember they have a duty to look after the interests of their citizens.
A high risk strategy is to allow the Italians to try again, because they have shown a strong propensity to convict against the publicly available evidence.
What is the appropriate thing for the State Department to do?
The fact there followed an unprecedented judicial act, and the Italians were playing with the life of a citizen of the most powerful nation, who know she is innocent, leads me to conclude the State Department did their duty.
Without more information it seems unlikely we can progress from here however.