I did say the studies 'tend' to support and are not conclusive.
Anyway, here are 2 quickies for you to peruse.
From Animal Cruelty to Serial Murder: Applying the Graduation Hypothesis
another one
There are plenty of studies that tend to suggest that people who exhibit psychotic tendencies, and also those who become mass murders, were also cruel to animals in their youth. Whether it is the cruelty to animals that desensitises them or the fact they are evil fucks that makes them abuse...