According to the FBI, some 33,000 violent street gangs, motorcycle gangs, and prison gangs are criminally active in the U.S. today. Many are sophisticated and well organized; all use violence to control neighborhoods and boost their illegal money-making activities, which include robbery, drug and gun trafficking, prostitution and human trafficking, and fraud. Many gang members continue to commit crimes even after being sent to jail. On the front lines, law enforcement battles everyday to keep communities safe. This is their story.