There is actually a really good section in the book "Some We Love, Some We Hate, Some We Eat" about the (alleged) link between serial killers and deliberately torturing animals in childhood. Like most studies... it comes up with mixed results - some suggest a link, others do not. One thing that stood out to me is that several studies have shown that
most children will at some point partake in and potentially enjoy cruelty to an animal - for example, pulling wings from moths, pouring salt on slugs, blowing up a bullfrog, pulling a dog's ears and tail, etc. Some child psychologists feel it is prevelant enough to be considered normal childhood development, a form of healthy play, and part of the process of investigating and developing empathy, ironically enough.
Here is the difference, however: generally, when normal adults are polled about childhood abuse of animals, there is a common trend: most felt remorse for what they did, either at the time or later when they were old enough to have a sense of empathy. When violent offenders are polled about childhood mistreatment of animals, those who admit to it generally show two common trends: the severity of the abuse was more marked and generally involved an animal with higher societal value (ie. setting a dog on fire vs. squishing a caterpillar), and there was generally no remorse at the time of the abuse nor later in life.
So, while you can't really say that harming an animal is a reliable indicator that a child will develop dangerous behaviors as an adult, you could say that the nature of the cruelty and the child's reaction to it CAN be telling.
Would love to link to the actual aforementioned studies but they were cited in the book, so it's not as simple. Definitely a good section to read if the topic interests you though, and if you are super curious, write down the names of the studies and journals in the back of the book to assess it for yourself.
If I had it handy I'd jot them down so folks could look them up, but I'm at a public 'net spot rather than at home.
