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The advent of new technologies such as DNA typing, the weight of scientific evidence in criminal trials of widespread publicity, and the proliferation of fictional and non-fictional works in popular media have contributed to making forensic science well known, although perhaps not as well understood, by the general public. One of the consequences of this popularisation of forensic science was a sharp change in the attitude of investigators, who increasingly tend to delegate to scientists the collection of information necessary to identify the perpetrator of the crime. However, the prominent focus on the search of biological traces or fingerprints, due to their high potential for the personal identification of the individuals present at the crime scene, somewhat fade the interest towards other kinds of evidence, such as trace evidence. This kind of evidence is in fact perceived by judges and lawyers as less informative, because they think that \"all plastic items are the same\", i.e. that it is impossible to discriminate among mass produced items. The purpose of this paper is to stress that, with sound methods for interpreting evidence, it is possible to improve the communication between the scientist and the Court, and to show the real significance of the analytical results, in the context of the case. The analysis of the traces found on a knife used in a murder case were performed by optical microscopy, IR spectroscopy, and UV-visible spectroscopy. The interpretation of evidence was carried out according to a Bayesian approach. A description of the interpretation of evidence in a case in which fibres were the key evidence. It is shown that the key aspects for having a high value of the evidence are the circumstances of the case and the reconstruction of the events given by the prosecutor and by the defence, in addition of course to a sound analytical procedure. In other words, it is shown that in some cases the evidential value of fibres or other trace evidence can be very high, sometimes comparable to that of fingerprints or DNA: when properly interpreted, trace evidence can give key information for solving cases.

Fifty shopping bags, commonly encountered in the packaging of drug doses, were characterized by thickness measurements, infrared spectroscopy and differential scanning calorimetry. By these very straightforward and inexpensive techniques, without sample preparation, nearly all the considered samples could be discriminated. Ninety-seven percent of the possible pairs of white, apparently similar dull polymer films were differentiated. The rather large degree of variability existing in grocery bags, even though they are mass produced, was shown, confirming that these items can be useful in tracing the source of illicit drug doses.

Thirty-three shopping bags, commonly encountered in the packaging of drug doses, were characterized by wide angle X-ray diffraction (WAXD). Using this single technique, without sample preparation, nearly all the considered samples could be differentiated, achieving a discriminating power of 0.992. The rather large degree of variability existing in grocery bags, even though they are mass produced, was shown, confirming that these items can be useful in tracing the source of illicit drug doses.

Latex gloves are quite frequently employed by felons, when committing crimes, if they want to avoid shedding fingerprints or biological traces. Less forensic aware crime committers, though, may discard the gloves at the crime scene or nearby. If found and properly analyzed, these items may therefore provide useful information to investigators. An analytical procedure of such items is proposed, using thermogravimetry and differential scanning calorimetry. By these very straightforward and inexpensive techniques, without sample preparation, nearly all the considered samples could be discriminated. 99.5% of the possible pairs of latex gloves, indistinguishable by visual examination, were differentiated. The rather large degree of variability existing in latex gloves, even though they are mass produced, was shown, confirming that these items can be useful in comparisons between items related to the crime scene and those seized in the suspect's premises.

Fiber evidence found on a suspect vehicle was the only useful trace to reconstruct the dynamics of the transportation of two corpses. Optical microscopy, UV-Vis microspectrophotometry and infrared analysis were employed to compare fibers recovered in the trunk of a car to those of the blankets composing the wrapping in which the victims had been hidden. A “pseudo-1:1” taping permitted to reconstruct the spatial distribution of the traces and to further strengthen the support to one of the hypotheses. The Likelihood Ratio (LR) was calculated, in order to quantify the support given by forensic evidence to the explanations proposed. A generalization of the Likelihood Ratio equation to cases analogous to this has been derived. Fibers were the only traces that helped in the corroboration of the crime scenario, being absent any DNA, fingerprints and ballistic evidence.