How did speakers explain how they were able to commit atrocities?

Criminologists have developed many theories as to why people commit crimes. If you check the History Learning Site, it lists one prominent theory that explains how people are influenced by the environment around them, especially the environment they grew up in. Conversely, others believe that one's biology and genetics determine an individual's potential to become a criminal. Other theories suggest that humans are innately self-interested and will commit crimes if they perceive the benefits of the crime to be greater than the risks to themselves. Another theory maintains that people commit crimes based on their social environment and the people they associate with.