I don't necessarily agree with the old adage, "You can't write what you don't know." Now, you might write what you know better than how you write what you don't, but you can still accurately portray aspects of life without having lived them. I might have book knowledge of schizophrenia, but I don't have schizophrenia. I can still write about it.
Where I'm going with this is that we often have criminal behavior in our books, yet I would wager that most of you have have not been down that road yourself. So what do you then base your knowledge of criminal behavior on? Some action perpetrated against you or someone you know? Something you saw on TV and hoped would translate well into your work in progress?
I can't say I haven't done that, but I always fall back on psychology to help me out. (DISCLOSURE: I'm not a lawyer!!!)
From what I can understand, sane people commit crimes for two main reasons: they are selfish or selfless. Even though the criminal system doesn't put much stock in a person's motives unless most of the evidence is circumstantial, once a writer gets the motive down pat, writing just about any criminal behavior believable.
Motives are the causes/reasons that induce a person to form the intent to commit a crime. It's not the same thing as intent, which is the purpose of the crime. For example, my husband's truck was broken into yesterday morning while he was fishing the mouth of the Eel River (thus, the impetus for this post). Since we assume the criminal was a homeless man, the motive was to stay warm because he took a very nice and expensive Gore Tex wading jacket on the back seat. The intent was to vandalize the truck by breaking out the back window.
The way we figured the event out in our heads, this was a selfish criminal act, because we assumed the homeless person took everything for himself. But it could have been selfless if he was stealing that jacket for his little son living in one of the broken down vans in a makeshift village in that area. This is the same reason why a person would steal to feed or clothe their families.
I've really tried hard to think of some crime Even criminals who just kill to kill or steal for the "good times" are working from a selfish motive. The revelry serves a purpose in their life even if the actual criminal act didn't have much of a function. White collar crimes of embezzlement and fraud come from a selfish arena mostly, but a write could easily throw in a different, altruistic motive and have the reader actually hoping the criminal doesn't get caught!
(Just as aside, earlier I made a point to italicize that this applies to sane people only. Those with mental instabilities or retardation might commit a crime and not even realize they are doing it. The Latin phrase that translates "the act does not make a person guilty unless the mind be also guilty" is where the idea of mens rea, or "guilty mind," comes from. A mentally disturbed individual might have an actus reus, or the act of the crime itself, but not a mens rea.)
But I'm curious. Can you think of any crime that doesn't fit one of these two motives? Fair warning...I'll do my best to refute you in the comment section! :)