The likely scenario, to me, is that Thompson was just interested in violence, but he awakened something more sexually deviant in Venebales.

Depending on how it all went down Venebales might have even been a victim as well. Maybe if the whole horror never happens he never becomes interested in those things, maybe seeing what he did that day and then losing his freedom throughout his adolescence perverted his sexual growth somehow.

Thompson goes on to be repentant at the prospect of losing his freedom, gets proper guidance and makes the best of his (probably undeserved) second chance. Venebales is forever changed by the experience and remains obsessed.

I don't know, just speculating really.