Two or three components, the military had press with them.

Also, exploiting war crimes by the enemy for propaganda reasons was very important for morale, so it was a high priority thing to have writers and camera people available to document things.

Regarding distribution, specifically the Germans put the info into weekly cinema productions, en.wikipedia.org/wiki/Die_Deutsche_Wochenschau But there was also radio and newspapers.

Ultimately it depended on either the military or reporters uncovering it and then reporting it.

Japan did establish Unit 731

Not sure how that was in that case.