Paying for someone else's mistake: the effect of bystander negligence on perpetrator blame.

The success of criminal acts can sometimes depend critically on the oversight or negligence of uninvolved bystanders (e.g., someone leaving a first-floor window open). Four studies examined how the contribution of a negligent bystander affects blame for the perpetrator of a crime. Although participants stated that discounting blame for the perpetrator was normatively inappropriate in this context, they expected that others would make this very "error." Instead, across all four studies, bystander negligence amplified ascriptions of perpetrator blame. This amplification occurred because the bad action of the bystander provided an implicit standard of comparison for the perpetrator's act, framing it as more blameworthy. A variety of alternative mechanisms--that bystander negligence altered perceived crime avoidability, prompted spontaneous counterfactualizing, or increased victim empathy--were tested and ruled out. Implications for legal contexts are discussed.