Have you recently experienced a disruptive event or critical incident? Call now to get 24/7 support 888-736-0911

Understanding the Importance of Recognizing Warning Signs of a Mass Shooter


At approximately 6:30 a.m. this past Wednesday, a disgruntled employee of the VTA railyard named Samuel Cassidy entered the facility in San Jose and opened fire—killing at least 9 coworkers before turning the gun on himself as law enforcement closed in.

Gun violence overall is on the rise. Data from the Gun Violence Archive shows that since April 2020, there has been a significant increase in multi-victim shooting incidents. This increase has remained elevated throughout the year. According to the FBI, a mass shooting is defined as any incident in which four or more people are injured or killed. In 2021, the rate of mass shootings is markedly up, with 160 mass shootings in the U.S. to date, compared to 90 occurring within the same time window from 2020. Furthermore, the incidence rate of mass shootings in 2021 is almost double the yearly average seen from 2014 to present. Simultaneously, we are seeing a trend of mass shootings resulting from lower profile interpersonal disputes of a highly emotional nature–family feuds, domestic relationship disputes, and conflict arising during private home events—as opposed to assailants with only surface-level or tangential emotional connections through work settings.

The San Jose shooting echoes the latter, with common patterns seen when a disgruntled employee harbors a sustained grievance mixed with high levels of rage and the sense of feeling they were unfairly treated.

Understanding the Warning Signs of a Mass Shooter

It is hard for anyone to believe that someone they know or love is capable of committing a mass shooting.

However, those of us with expertise in the threat management arena know these cases often show common red-flag indicators, sometimes present years before the attack. It is important to recognize red-flag indicators, as these tragic events are on the rise.

In the case of Samuel Cassidy, we now know there were a host of red flags—all of which were clearly demonstrated in the forensic literature as risk factors for targeted violence. Cassidy’s red flags included a past encounter with the law, angry outbursts, voiced threats to the workplace, violent ideation and obsession with retribution; domestic violence, sexual assault, inadequately treated mental illness, excessive alcohol use, and a fascination with collecting weapons.

To complicate matters, it is difficult to determine which of the select few individuals showing warning signs will go on to act violently, as most people will not. Furthermore, the ability for any informed person or expert to gain access to knowledge of these risk factors before action occurs is statistically quite small. Information often emerges and remains in silos, resulting in authorities underestimating a given risk instead of taking preventative action against the individual demonstrating red flags.

Reporting the Warning Signs of a Mass Shooter

While not everyone who complains about work or makes violent remarks becomes a mass shooter, it is crucial to report these concerns if one observes an individual demonstrating these behaviors in the workplace or at home. When doing so, it is important to report concerns to those in a position of authority or with the power to intervene (i.e. HR, security, senior management, legal team, internal threat management team, treatment providers, or law enforcement). The question of who to report such information to, and the method of doing so, will vary per organization, location, and industry. It remains critical to share this information so that an investigation (and proper intervention if needed) can occur.

The harsh reality is that almost all targeted mass shooters are struggling in some capacity. In Cassidy’s case, aside from years of likely personality disturbance, anger management issues, mental illness and alcohol use, we know that he felt (rightfully or not) unfairly treated by his employer. His ex-wife, Cecilia Nelms, reported to the AP that Cassidy discussed harming others at work almost ten years ago, in addition to displaying a pattern of coming home from work angry over feeling misunderstood and unfairly treated by managers. Nelms also reported, “he could dwell on things.”

In no way do these struggles absolve Cassidy’s actions or lay blame on his employer. This is not a question of who is right or wrong, it is a pragmatic question: how do we identify the risk factors and emotional trigger points of someone on a trajectory of violence, so that we can redirect them off that pathway and towards adaptive, non-violent coping options?

In the field of threat management, we call people such as Cassidy “grievance collectors”, as they show a pervasive pattern of never letting resentment from an offense go, often holding on to it for years. In my work as a certified threat manager, I have been fortunate to identify these individuals early on in their potentially dangerous paths—prior to them becoming violent—so that I can intervene and redirect them to other methods of conflict resolution. All of these methods are case specific, but the key is to first identify individuals showing red flags and behaviors of concern and then direct them to the proper resources and threat experts who intervene and defuse the situation. When executed correctly, this process works—consistently and well.

As a global leader in workplace behavioral health, crisis, and security solutions, we help to ensure the psychological and physical safety of organizations and their employees. For more information and support in addressing concerns of potential violence, check out our Protective Services. If you’d like to connect with us right away, you can do so here.

Helping People and Organizations Thrive

Workplace behavioral health is more important than ever. R3 provides innovative, tailored solutions to cultivate it.

Skip to content