For me there is only one thing left " against " the legacy pilots : did one of them swich the Xponder off voluntarily , or did the Xponder went automativcally on stand by as did some of the little brothers of the Honeywell Primus in Europe recently ?
The problem as I understand it ( and someone correct me if I am wrong ) , is that the Legacy FDR does not record the Xponder inputs , just the fact that it is ON , SBY or OFF. And that info is in the hands of the FAB / CENIPA since quite a while.
If nothing can be proven then , in my opinion,the doubt should benefit the defendants, and the 2 guys should be left alone and allowed to return to their homes.
The other suggestions/ claims that they did not follow the valid comm failure procedure in force is vague ,and is in any case not a voluntary act, not even gross negligence, just ignorance, and does not justify their further retention , again in my opinion..
I am also surprised at USALPA silence in this case.