That begs a question: isn't there a single DOJ employee willing to out the memo setting the no-prosecution-of-black-on-white-as-hate-crime policy? Or was it all word of mouth?
At most, there may be some internal email(s) implying such; doubt there are any official missives to this effect.
Besides, we all know bureaucrats treasure their cushy jobs far more than the Constitution or the well-being of the American citizenry (especially if you’re a white citizen).