Policymakers seeking to counter the rise of U.S. mass shootings after Parkland, Florida, are looking at everything from gun laws to mental health, but there is no obvious legislative fix for the Columbine effect.

The 1999 Columbine High School massacre gave rise to a fascination with the two teenage killers and mass shootings in general, spawning a social media subculture and inspiring dozens of disturbed young men to seek fame and vengeance by emulating their deadly heroes.

“Columbine was not the first modern school shooting, but it put school shootings on the map,” said Jeff Kass, author of the 2009 book “Columbine: A True Crime Story.” “In that sense, it’s a really tough and sad thing to say, but I think Columbine opened the door not only for these school shooters, but the adult mass shooters as well.”

Psychologist Peter Langman keeps updated on his SchoolShooters.info website a diagram of U.S. mass shooters who credited Columbine as an influence. So far, the count is 33.