As mentioned in the article, there are many theories of why someone becomes a criminal, but it is generally agreed that it is a combination of genes, events, conditioning, and personality. It has been shown in studies with twins that identical twins are more likely to share criminal tendencies than non-identical (or fraternal) twins. This might indicate a genetic link, as identical twins have more genetic similarities, but also that personality is involved, in the case of the fraternal twins. There also is a theory that where siblings come in the family can have an effect on their behavior. For example, middle children often show more challenging behaviors and it's theorized that it is because they are trying to get attention. I'm not a forensic psychologist, so that is about the limit of my knowledge.