Author Dave Cullen, in his 2009 book "Columbine" on the infamous 1999 Columbine High School massacre and its perpetrators Eric Harris and Dylan Klebold, described Harris as an “injustice collector.” He expanded on the concept in a 2015 "New Republic" essay on injustice collectors, identifying several notorious killers as fitting the category, including Christopher Dorner, Elliot Rodger, Vester Flanagan, and Andrew Kehoe. Likewise, mass shooting expert and former FBI profiler Mary O’Toole also uses the phrase “injustice collector” in characterizing motives of some mass shooting perpetrators. In relation, criminologist James Alan Fox contends that mass murderers are “enabled by social isolation” and typically experience “years of disappointment and failure that produce a mix of profound hopelessness and deep-seated resentment.” Jillian Peterson, an assistant professor of criminology at Hamline University who is participating in the construction of a database on mass shooters, noted that two phenomena surface repeatedly in the statistics: hopelessness and a need for notoriety in life or in death.