I have a degree in biology, and a strong interest in this topic.
Most research seems to be in the area of testosterone and serotonin levels.
I am finally in graduate school and hope to learn alot more. I have just recently begun my study on the causes of criminal behaviour however what has been made very clear thus far is that biological factors do play a very important role in this development. I have come across numerous studies done in Northern Ireland which show that this point is infact true. In these studies twins were seperated at birth, they were both placed into families with no criminal backround yet still showed extreme criminal behaviour. There are many more instances which also show just how apparent biological factors are.