What would stop a government from making something "classified" ex post facto just to silence and/or jail nay-sayers, political opponents, or oppressed peoples? The answer is nothing, and this is exactly why this cannot stand.
Even the damnable rhetorical justification for abuses "fire in a crowded theater" standard of nuclear launch codes this applies to - since if they were compromised let the whole goddamn world know it is 1-2-3-4-5 so that they can have actual security instead of illusion of security and the fuck ups responsible being safe from any deserved backlash.
However that may be, sloppy/negligent editorial work i.e. the release of names (uncensored) can very well be a judicial issue -- but that is not what he is accused of. And it should definitely not be persecuted with the remnant of a war-time power grab [espionage act].
War crimes are no valid secrets and there was no legitimate channel. You would be ethically required to act and leak the information.