In the two decades since the massacre at Columbine High School, digging into the psychology of mass shooters has sadly become an all-too-familiar habit — now something we seem to do almost weekly.

After the Virginia Tech shooting in 2007, media coverage pointed to the shooter’s odd behavior as a child and his near-mutism as a college student. After the mass shooting at Sandy Hook Elementary School in Newtown, Conn., in 2012, newspapers described the shooter as “withdrawn and meek” and suggested that he might have had Asperger syndrome. The two people responsible for the shooting at STEM School Highlands Ranch in Colorado on May 7 are already the subjects of forensic investigation of their presumed troubled pasts.

This practice is not just a phenomenon of the post-Columbine era of mass shootings. It has its roots in the early 20th century, and it represents an effort to shift blame and find an area of consensus after massacres that could otherwise force uncomfortable conversations. In the process, this practice fosters stigma against one of the most vulnerable groups of Americans: the mentally ill.

In the late 19th century, reports of mass shootings were typically very brief. But by the turn of the century, coverage grew more detailed, often describing how the shooter had gone “suddenly insane” as a result of financial losses or a romantic mishap.

Starting in the 1930s, newspaper coverage of shootings expanded. Journalists and those affected by the shootings searched for clues in the shooter's past that might explain why the tragedy took place. They used the Freudian language of “complexes” that had become a part of daily conversation and the psychiatric language of diagnostic categories to offer an answer.