羅卡交換理論：凡接觸過，必留下痕跡。因此暴力與性犯罪必然留下生物跡證，侵入住宅竊盜也常見體液或毛髮遺留在犯罪現場，而屍體殘骸可能是命案的被害者，死者肺臟與蝶竇液之矽藻更是研判溺死或棄屍的關鍵證據之一。這些生物跡證的搜尋需要特定方法，而鑑定方法則大都採用分子生物技術，其準確度高，可有效提升司法審判的品質。本文提供常見法醫生物跡證鑑驗方法之介紹，以見證科學證據之可靠性。

Locard᾿s exchange principle states that every contact leaves a trace. Therefore, there could be biological evidenceleft during assault or sexual crime, and fl uids or hairs could also be seen in residential burglary cases. Furthermore,body parts of remains may be linked to a victim. Diatom identifi cation from body's lung tissue or sphenoid sinusfluid is a key evidence of drown or foul play in death investigation. We perform specific ways to find possiblebiological evidence, and molecular biology techniques are often used. Its high degree of accuracy will improve thequality of criminal justice. This report provides common examination methods for biological samples of forensicmedicine to demonstrate the reliability of scientifi c evidence.