In the field of psychology people who kill animals in their youth are flagged as psychopaths, with a career of killing humans a likely scenario of their adult life.
Psychopaths are charming, oftentimes successful people who have absolutely no moral compass.
This is scary stuff.
Obviously showing blood and gore is not the way to touch the hearts of animal lovers. This is a human interest story, not a funny and not a snuff movie. Any portrayal of this should be sad, and no other emotion should be involved.