Getting interviews with people who have violated the law for whatever reason can be an important element of your documentary. Your topic may cover issues that are not always addressed in a culturally accepted fashion, and often times people break social standards to further their objectives. These things can play together in your dramatic film prose and end up highlighting a large conflict. To get some of these interviews you may have to actually address the people while they are incarcerated, which is one of the hardest locations to get an interview from.