Was the rape thing known?
It probably was.
We talked a lot about his beatings of prostitutes, which was him directly. Our general consensus was that the team surveilling him should have intervened on that and politics be damned.
Abernathy was --- as I remember--- hated and shunned by the Civil Rights establishment for talking openly about it.
Even before that, a classic autobiography --- "Coming of Age in Mississippi" --- published in 1968 --- discussed the demoralization author Anne Moody suffered as a young black woman when she realized that idealistic advocates like herself were being sexually exploited by the black male leadership.
I don't remember if she accused MLK by name or not, but I do remember she painted a picture showing that the callous abuse of women was rather widespread.
It pains me to relate this. There was much in the 1950's and early '60's Civil Rights movement that was dignified in the highest degree. It's a shame that its nobility was defiled by behavior --- by some --- that was frankly bestial.