Table 1 Decision criteria to select the features to profile. Intrinsic criteria (relative to the features themselves and their origin) Extrinsic criteria (relative to the observation and measurement methods) Low intra-variability: no or low variation among traces of a same origin Non destructiveness: must not alter the trace integrity Sensitivity: ability to return a positive result when the feature is present High inter-variability: significant variation among traces of different origins Specificity: ability to return a negative result when the feature is absent Complementarity: the features must be as independent as possible Reproducibility and reliability: consistency of results when the extraction/acquisition operation is executed by different operators or equipment, at different times or locations Representativeness: reflects the features and traits of the source(s)/ activity(ies) at the origin of the trace (materials, equipment and method used) – as far as a person comes into question, privacy issues must be taken into account Low resource requirement in terms of costs, time, equipment, knowledge and training since the extraction/ acquisition operation will be repeated for each new trace Comparability: features of a given trace must be comparable to the features of the others to evaluate their similarity/dissimilarity Accessibility: equipment and knowledge available to stakeholders that are prone to operate the profiling task – reciprocally, traces accessible to stakeholders who possess the required equipment and knowledge to operate the profiling task Availability and completeness: the feature is constantly and completely observable/measurable in the population of interest (all the traces considered) Adaptability: ability to follow-up on the evolution and mutations of the observed/ measured feature