Explain its role in justice.

Physical evidence — the material traces of the crime: the objects carrying the information (against the testimonial evidence's words). The types: biological (U4-U5: the blood, the semen, the DNA); impressions (U3: the fingerprints, the footprints, the tyre marks); trace (U6: the hair, fibres, paint, soil, glass); the arms-and-tool marks (U10); the documents (U9); the digital (the devices-and-data); the chemical (U7-U8: the toxins-and-drugs). The importance's core: the objectivity (no motive-to-lie), the memory (the evidence persists when memories fail), the corroboration-and-contradiction (the testimony's test), the reconstruction (the event's scientific rebuilding).