범행동기를 암시하는 증거는 범행을 입증하는 증명력이 거의 없다. 그럼에도 불구하고, 인간의 확률추론에 개입하는 인지적 편향성에 의해 범행동기를 암시하는 증거의 증명력이 주관적으로 높게 평가되고, 종국적으로 오판이 초래될 위험을 높인다는 주장이 제기되었다(Davis & Follette, 2002, 2003). 본 연구는 이 주장의 타당성을 확인하고, 범행동기 증거의 주관적 증명력이 평가되는 방식에 대한 이론적인 이해를 획득할 목적으로 수행되었다. 131명의 20대 참가자들은 아내를 살해한 혐의를 받는 피고인의 재판시나리오를 읽고, 피고인이 유죄일 확률, 유무죄 여부 및 범행동기를 암시하는 증거의 증명력을 평가하였다. 재판시나리오는 세 수준(약, 중, 강)으로 조작한 범행동기를 암시하는 증거를 제외한 다른 증거들의 강도와 두 수준으로 조작한 범행동기를 암시하는 증거의 제시 여부가 교차되어 제작되었으며, 피험자간 설계가 사용되었다. 참가자들은 범행동기 증거가 제시되어도 유죄판단을 더 많이 하거나 유죄확률을 더 높게 평가하지 않았다. 이것은 범행동기 증거의 증명력이 확률추론에 기반하여 평가된다는 증거가 없음을 나타낸다. 반면에 범행동기 증거의 주관적 증명력에 대해서는 정합성기반의 추론 모형의 예측에 부합하는 양상 즉, 재판에서 제시된 다른 증거들의 강도가 피고인의 유죄에 대한 심증에 영향을 주고, 유죄심증이 다시 범행동기 증거의 증명력 판단에 영향을 주는 정적 경로가 명확하게 확인되었다. 논의에서는 범행동기를 암시하는 증거의 증거능력에 대하여 논의하였다.
Pieces of evidence that implicate the motive of the defendant for committing the alleged crime do not in itself prove the guilt of the defendant. Davis & Follette (2002) raised a concern that judges and juries would rely on the representativeness heuristic to evaluate the motive evidence and thus, overestimate its probative value which could lead to an erroneous conviction. The present study was to see whether the probative value of a motive evidence is indeed overestimated and to acquire an understanding of the way in which the probative value of a motive evidence is subjectively evaluated. One hundred thirty-one participants in their 20s read a trial scenario of a murder case in which the defendant was charged for a uxoricide. The participants rated the probability of guilt, rendered the verdict, and evaluated the probative value of the motive evidence (infidelity of the defendant) presented by the prosecutor. The trial scenario was manipulated into three levels of the strength of evidence (weak, medium, high), and each level was divided into two conditions, one with the motive evidence and the other without the motive evidence. The participants in the condition with the motive evidence did not render more verdicts of guilty nor rated the probability of guilt higher than the participants in the condition without the motive evidence. On the other hand, the participants' evaluation of the probative value of the motive evidence showed a pattern predicted by the Coherence-Based Reasoning Model (Simon, 2004; Soriano, 2003). Specifically, the strength of evidence affected the participant's conviction about the defendant's guilt and the conviction, in turn, affected the evaluation of the probative value of the motive evidence. Finally, we discussed the admissibility of the motive evidence.
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