The motive remains unclear.
As does the motive for why Roy's tiger decided to rip him to shreds one day. The tiger "went tiger" and the nigger will ALWAYS go nigger. Tigers should be left in the wild, as should niggers. Neither of these are pets.

You do not have nigger friends, boy/girlfriends, business partners, baby daddies, roommates, or tenants. They will attack you. The only question is "when". If you think calling them friends or associates will protect you, better think again.

Williamson Was Initially Welcomed Into the Home But Attacked Matthews With a Hammer
Well... yeah.