A wide variety of data sources shows gross differences in the treatment of potential capital offenders by race of offender and victim and by judicial circuits within States. These differences are (1) independent of aggravating felony-related circumstances, (2) present at both presentencing and sentencing stages of the criminal justice process, (3) uncorrected by the postsentencing appellate review process, (4) unaltered by the form and restrictiveness of capital punishment statutes among States, and (5) remarkably similar to the best documented patterns of differential treatment by race of offender and victim under pre-Furman capital statutes, now ruled unconstitutional. The findings indicate that the present system of capital punishment is inconsistent with the constitutional standards of the Furman and Gregg decisions of the U.S. Supreme Court but is instead consistent with historically prevailing extralegal influences which compromise and displace the legally prescribed functions of such punishment and are an enduring source of arbitrariness and discrimination. Adjustment procedures for temporal and cross-sectional undercoverage of homicide offender data are discussed in an appendix, and data sources and 96 footnotes are provided, along with tabular data. (Author abstract modified)