A Short Circuited Brain

So I've been thinking lately about criminals and stuff. You hear and read about crime that happens in the world everyday and I wonder what makes criminals do the things that they do? I started thinking about myself when I was younger and I had the urge to steal things. The things I stole wasn't valuable it was small things like bubble gum and what not. To be honest I don't even know why I stole those things my family always provided me with everything that I needed. Come to think of it I probably stole those things out of the pure fact that I didn't have it or simply because I had the urge for something new. Although those things were small stealing is stealing but it really makes me wonder why people start committing much larger crimes. I did it simply because I wanted to and because I didn't have those things but what makes a killer kill? and a rapist rape? Are they the same as me and do those things because they want to? Or perhaps there's something psychologically wrong with them. Some people go wrong because of a bad past. I hate it when people say they understand someone when they really don't. You can never understand a person until you've gone through the same pain that they have. I'll probably never understand criminals because they all have their different stories.