This study looks at the principles that shape the structure of the whole of Thai criminal procedure law. It examines how the search for truth is attempted to be reconciled with the idea of a fair trial or procedural fairness. The conflict between the search for truth on the one hand and guaranteeing procedural rights of the accused on the other is particularly problematic in the Thai context. Thai law affirms that some evidence cannot be admissible if it is obtained by a violation of certain procedural norms. At the same time, the law allows judges to admit some unlawfully obtained evidence in the interest of justice. The conflict between various legal norms cannot be solved without permitting judges to exercise broad discretion in striking the right balance between discovering the true facts and protecting the rights of the accused. Thai legal education and practice does not allow a broad judicial discretion in accepting or rejecting evidence on the grounds that it was obtained unlawfully. As a result, there is an attempt to build a sophisticated system of rules to accommodate the interests of justice and fairness in different situations. This system, however, lacks clarity and consistency.