From Locard to Court: The Scientific Foundations and Legal Admissibility of Firearm Evidence in Court

Background/Objectives: Despite its central role in murder investigations, firearm evidence remains one of the most scientifically contested and legally scrutinised forms of forensic proof. International critiques have highlighted limitations in foundational validity, examiner subjectivity, and individualisation claims within firearm and toolmark analysis, underscoring the importance of examining these issues within the South African context. Despite its central role in murder investigations, firearm evidence remains one of the most scientifically contested and legally scrutinised forms of forensic proof. Firearm evidence remains central to murder investigations; however, ongoing scientific and legal debates continue to raise concerns about its reliability, interpretation, and admissibility. Materials and Methods: A qualitative case study approach was used to examine the scientific basis, forensic integrity, and legal admissibility of firearm evidence. Semi-structured interviews were conducted with 39 purposively selected participants, including detectives, crime scene experts, and ballistics specialists. Participants were drawn from Tshwane-based police stations with high murder rates, using a combination of purposive, random, and systematic sampling techniques. Guided by interpretivist and constructivist paradigms, thematic and content analysis were applied building inductively on the empirical findings and informed by contemporary international debates. The study developed the Triadic Model of Forensic Investigation: Science, Integrity, and Law, integrating scientific, procedural, and legal dimensions of firearm evidence. Results: The study examined the Locard Exchange Principle as the scientific foundation of firearm evidence and found varying levels of practitioner understanding. Although some participants demonstrated foundational knowledge of forensic concepts such as identification and individualisation, terminology and conceptual understanding varied substantially across professional groups. Understanding of chain-of-custody requirements and legal admissibility criteria was uneven, with notable gaps among some practitioner groups. These inconsistencies, particularly among Investigating Officers, have significant implications for evidentiary integrity and courtroom reliability, especially in contexts where courts increasingly scrutinise categorical claims of firearm source attribution. Conclusions: The results highlight the importance of aligning professional practice, forensic education, and evolving scientific and legal standards to support reliable and legally admissible firearm evidence. The Triadic Model provides a coherent evaluative structure for strengthening the reliability, interpretive accuracy, and legal defensibility of firearm evidence. The study emphasises the value of interdisciplinary collaboration and closer alignment between forensic science, operational practice, and evolving judicial standards.