Although it is important to know what public mass shooters have in common, it is also helpful to understand when different variables were present on their pathways to violence. This study explored the timing of key life events for the deadliest public mass shooters in the United States since Columbine (N = 14). Using data from official reports and supplementary sources, we found perpetrators' mental health contacts often began more than a decade before their mass shootings, and often ended more than a year before their attacks. Mental illness was typically a constant in their lives, not something that automatically caused them to attack. While treatment may help prevent some mass shootings, mental health professionals have limited influence over patients they have not recently seen. In turn, perpetrators' work and school problems also typically began long before their mass shootings, but these issues continued closer to their attacks. Employers and educators may therefore have an opportunity to intervene later in the process. Firearms acquisition often occurred in the final stages, after perpetrators were already interested in mass murder. Red flag laws and ERPOs which prohibit sales to explicitly dangerous individuals may therefore help reduce the prevalence of these attacks.