According to a recent study by Prof. David Sloss of the St. Louis University School of Law, and others, only a small percentage of eligible murder cases in Missouri are prosecuted as death penalty cases, and even fewer result in a death sentence. Only 2.5 percent of defendants prosecuted for intentional homicide are sentenced to death. In another 2.5 percent of cases, juries reject the death penalty. Ninety-five percent of intentional homicide cases are never presented to the jury as capital cases. But rather than depending on which are the worst crimes, the chance of a death sentence appears to rest more on what part of the state the crime was committed in.

According to Prof. Sloss:

Prosecutors in St. Louis County pursued capital trials in more than 7 percent of their intentional homicide cases. In contrast, prosecutors in Jackson County (Kansas City) pursued capital trials in fewer than one-half of 1 percent of their cases. These disparities raise the disturbing possibility that decisions about who lives and who dies may be guided more by the philosophical predilections of individual prosecutors than the culpability of individual defendants.

To lessen the effect of geography and the leanings of individual prosecutors, the authors of the study recommend a narrowing of the class of cases eligible for the death penalty.
(David Sloss, “Death penalty: In Missouri, where you live may matter,” St. Louis Beacon, May 1, 2008). See Arbitrariness and Studies.