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Police are working to uncover the motive for a 16-year-old student who opened fire at his high school in Santa Clarita on Thursday, killing two classmates and injuring three others and himself. Many who knew the shooter are reportedly shocked that he perpetrated the crime, but in many ways he fits the profile of K-12 shooters. Forum talks with a sociologist who has studied the 171 mass shootings in public spaces since 1966 and found that there are five types of mass shooters, depending on where the crime took place. We'll discuss what we know about mass shooters and whether the information can help prevent acts of mass violence.