The hidden face of crime scenes: a review on microtrace

Introduction: Microtrace consists of materials of different nature that can be found in crime scenes, being difficult to see with the naked eye, due to their submillimetre, submicroscopic or microscopic dimensions. Objectives: This work aimed to address the characteristics of the main types of microtrace found in crime scenes. Material and Methods: As a research methodology, publications exclusively in the format of scientific articles were sought, indexed in the Web of Science and ScienceDirect databases, using the terms microtrace and trace evidence. Results: Microtrace are classified according to their organic origin (fingerprints, diesel and biodiesel, hair, wood, microscopic plant origin and natural fibres), natural inorganic (microfossils, minerals and soils) and anthropic inorganic (bricks, paints, glass, plastics, synthetic fibres, gunshot residue and paper), and can reveal crucial information at crime scenes, depending on the technique used to process it (e.g., inductively coupled plasma, infrared spectroscopy, gas and liquid chromatography, micro Raman spectroscopy). In this way, laboratories must meet specific requirements, regardless of the analytical technique to be used, to extract reliable information from microtrace. These requirements consist of: 1) Accuracy, 2) Sensitivity, 3) Uniqueness, 4) Association, 5) Speed and simplicity, 6) Versatility, 7) Reliability and reproducibility, 8) Traceability, 9) Accessibility, and 10) Availability of data. Conclusions: This work highlighted the diversity and importance of microtrace, since extracting information from them can give them great potential as material evidence in criminal investigations, depending on the applied collection methods and the techniques used in their laboratory examination.