Artificial intelligence (AI) has produced many applications in various fields such as education and entertainment. One classical example is the expert systems used in medical contexts for making judgments about diagnoses, e.g., MYCIN (Shortliffe, 1977). Rule-based systems are commonly used to support human cognition and social decision-making. In this study, we focus on how AI can support a jury’s decision process in court. In Japan, the Ministry of Justice has introduced a mixed jury system for criminal justice trials, where citizen judges discuss and make decisions about the verdict and decide the sentence length in criminal cases. In such cases, the citizen judges are allowed to see objective data from similar past cases, and therefore it is possible to use the existing database to support the decision-making process. In this new project, in collaboration with psychology experts and computer scientists, we investigate how a juror’s decision can be supported by AI technology that provides data regarding sentences prior to decision-making.