动机不明的 meaning in English

unmotivated

He always wins cases in the court and helps the suspects escape from prison terms . will there be a hidden side for an arrogant person like him ? everyone in the story seems to possess some qualities that don t suit their identity
事实上，这里的每一个人都各自有著一点点不容于本身职业的性格特色，与此同时，城中亦不断发生著其他罪案，动机不明的凶杀案失踪案比比皆是，这些无头公案有可能与我们三位主角拉上关系吗？