I've read that people who do sick things like this to harmless animals are also the ones most likely to harm children.
But that's OK. I think that Karma has a way of giving people what they deserve before it's over with.
It is part of the triad of serial killers. A lot of serial killers started out with harming small animals mice, cats, rodents, dogs, the such, and later on would move on to humans.
The other two part of this triad is bed wetting (up to ages of 12-14) and pyromania, setting things on fire, little things and graduating to bigger things.
There are many other characteristics of a serial killer. However, this is known as the triad of serial killers.