A study examined the effects on mock jury decision-making of defendant motivation, physical ability, and opportunity to commit a crime by manipulating each in a 2 x 2 x 2 factorial design. 112 jury-eligible participants were randomly assigned to read one of eight versions of a hypothetical murder scenario and were each asked to render a verdict, to recommend a sentencing option, and to make other evaluative judgments of the defendant. It was hypothesized that all three factors would be important to establish guilt. However, since motivation is merely a sufficient condition for guilt, whereas ability and opportunity are necessary conditions, motivation was expected to have an effect only when both ability and opportunity were demonstrated. Log linear analysis confirmed that all three factors influenced mock jurors' verdicts and sentencing options. While the expected interaction between motivation and the other two factors was not obtained for criminal verdicts, sentencing options were affected by motive only when opportunity was also present. Analysis of variance confirmed that motive, ability, and opportunity also affected judgments of criminal responsibility, but personal evaluations of the defendant were influenced only by evidence of motivation. Results were discussed in terms of implications of these three factors for prosecutors and defense attorneys in criminal proceedings.