Of the 32 states with the death penalty, 25 states identify some variation of “heinous, atrocious, or cruel” as a statutory aggravating factor. In recognition of the vague nature of this factor, some states have enacted legislation that limits jurors’ discretion by providing guidance regarding how to define “heinousness,” or by outlining essential characteristics of heinous crimes. Despite this guidance, indiscriminate application is still a concern. Research has explored how heinousness affects juror decision-making, sentencing outcomes, and perceptions of the defendant; however, these studies have varied in their definitions and have not always ensured that perceptions of heinousness were different across conditions. The purpose of the current study was to better understand what elements of crimes are viewed as more or less heinous in the eyes of undergraduate mock jurors. Using a within-subject, vignette-based design, ratings of heinousness were collected for 53 vignettes and eight variables were studied (i.e., method of killing, relationship, victim age, victim vulnerability, mental suffering, physical suffering, gruesomeness, and time). Significant differences were found within each factor (p < .001). Results provide researchers with a framework for future heinousness research, as well as information for the legal system with regard to what constitutes heinousness.