As mass shootings have become ever more familiar, experts have come to understand them less as isolated expressions of rage and more as acts that build on the blueprints of previous rampages.

Experts in violence prevention say that many, if not most, perpetrators of such shootings have intensively researched earlier mass attacks, often expressing admiration for those who carried them out. The publicity that surrounds these killings can have an accelerating effect on other troubled and angry would-be killers who are already heading toward violence, they say.

The killing of nine people at an Oregon community college last week was a textbook example. Before opening fire, the gunman, Christopher Harper-Mercer, 26, reportedly uploaded a video about the 2012 massacre at Sandy Hook Elementary School in Newtown, Conn.

The perpetrator of the Sandy Hook murders was himself a student of earlier shootings — in 1999 at Columbine High School in Colorado, where 13 people were killed, and in 2011 in Norway, where 77 people were killed.