To expand on my previous comment regarding solutions and why intervention can be quite effective. There is a pretty decent blog post on Psychology Today about the causes of violence and why suggesting that people "just snap" is not helpful.
"The findings revealed that targeted violence is an often discernable process of thinking and behavior (they don't just snap). Assassins and attackers plan their attacks and are motivated by a wide range of issues. They consider several targets before acting, but rarely direct threats either to the target or to law enforcement. The findings also suggested that mental illness is not critical to determining dangerousness; the ability and capacity to develop and execute a plan is much more significant. Most importantly, the findings indicated that there is no "profile" of the attacker, but rather, identified a common set of "attack related behaviors" exhibited by the subjects. These behaviors are cited in the report.
Mental illness alone does not increase the risk of violence, but when mental illness is combined with other risk factors such as substance abuse, (as in the case of Bedell, who self-medicated with marijuana) it does increase the risk of violence. Previous research has produced mixed results about the link between mental illness and violence."
"Other factors that predicted violent behavior included a
- history of juvenile detention or physical abuse,
- having seen parental fighting,
- recent divorce,
- being victimized themselves.
- being younger, male, and low-income"
"Whether a person is mentally ill or not, one does not just "snap." There is generally a progression of behaviors down a pathway toward violence and those behaviors often become noticeable as a person moves down that path. As parents, teachers, friends, family, co-workers, and law enforcers, we should learn how to recognize those behavioral warning signs and communicate our concerns to people who might be able to help. Unfortunately, it can be extremely difficult to get help for someone with mental illness that doesn't accept the help, as was the case with Bedell."