In fact, I was told by one reader that people don't do things without motives - there's always a thought process and a decision (barring, I assume drugs and alcohol, mental illness, etc). I'm not sure about that. I am sure that sometimes it is impossible to know the motive - for instance, if the perpetrator is never found. Then, though there may have been a thought process involved, no one is privy to it.
Anyway, read the stories. Tell me what you think.