1.2 Principles of Forensic Science

1. Locard's exchange principle — "every contact leaves a trace": the perpetrator brings something to the scene and takes something away (the discipline's foundation). 2. The individualisation principle — the trace's unique source (the fingerprint's, the DNA's, the tool-mark's identification). 3. The comparison principle — the unknown-and-known's side-by-side (the class-and-individual characteristics). 4. The probability's discipline — the evidence's strength stated scientifically (the certainty's honesty — the probabilities, not the absolutes). 5. The integrity's chain — the evidence's custody-and-handling (U2.3). 6. The neutrality's ethic — the examiner's objectivity (the expert's duty to the court, not the client — U11).