But if someone has a clean record, how do you know they are dangerous? Unfortunately, some of the most sophisticated people who have committed some of the most heinous crimes have gone undetected because they pass background checks, and polygraphs, and don't set off any "red flags". They don't stand out. They work with the community, they volunteer...they are around those who are most vulnerable. I think those that are undetectable are more dangerous than the known ones that you expect to be on guard around. Because you don't know who they are.