San Diego shooting shows disturbing trend of shooters copying acts of violence

Experts say hate-motivated extremists being radicalized online and adopting ideologies of shooters before them

The killing of three men at a San Diego mosque on Monday is the latest example of a disturbing trend in recent decades: hate-motivated shooters learning from - and copying - each other in acts of violence meant to push the nation toward a race war and, ultimately, societal collapse.

The two San Diego shooters, who were 17 and 18, killed 51-year-old Amin Abdullah, a security guard at the Islamic Center of San Diego, 78-year-old Mansour Kaziha, a mosque elder and founding member of the center, and Nadir Awad, 57, who lived across the street and whose wife worked as a teacher at the center's school.