What we know and don’t know about how mass trauma affects mental health

Researchers are trying to figure out who is most at risk of self-harm

a group of students at a memorial in Parkland, Fla.

ONE YEAR LATER Thousands gather in Parkland, Fla., to remember the 17 students killed in a mass shooting a year earlier at Marjory Stoneman Douglas High School. Two recent suicides highlight the lingering trauma from the event.

Sun Sentinel/Tribune News Service/Getty Images Plus

In March, three people connected to mass school shootings died by suicide, raising questions about the lingering effects of such trauma on a person’s mental health.