Recent high profile legal proceedings have drawn attention to critical steps in the analyses which are able to provide invaluable evidence for the positive identification or exclusion of an individual as the donor of a biological trace in less complex cases.
The collection and proper preservation of biological evidence are critical to the success of the entire investigation and helps avoid contamination, one of the most problematic issues of forensic-genetic investigations.
Correct and rigorous preservation of the traces also ensures the best conditions for obtaining useful results.
Contamination occurs when traces of genetic profiles belonging to other individuals have mixed with the genetic profile under examination because of erroneous or anomalous processing of the evidence, thereby falsifying the result.
Anomalous processing may permit, for example, the transfer of the biological traces, or some of them, from the victim's to the suspect's clothing, and vice versa.
This may be the result of poor labelling, unsuitable preservation or even the accidental transfer of biological evidence from one sample to another during laboratory analysis.
It is therefore essential to adopt strict operational procedures, both at the crime scene and during the collection, labelling and preservation of the evidence, as well as during the laboratory tests.
The preservation of biological evidence
DNA is more resistant than many other biological molecules. However, it is exposed to the influence of various agents, whether chemical (colourants, detergents, acids, bases, etc.), physical (heat or light, especially ultraviolet rays) or biological (microorganisms). If the DNA structure is exposed to such agents over a prolonged period of time, it may be irremediably compromised.
After evidence has been collected, it is therefore necessary to protect it from chemical and physical agents and to avoid the proliferation of microorganisms by allowing to dry in the air if it is still wet or damp, and then by placing it in paper bags (not plastic) that should be placed in a refrigerated environment at the lowest possible temperature (freezer at -20°C/-80°C).
The legal investigation should be able to account adequately for all these aspects with suitable statements of collection, transfer, custody, seizure, etc.
Repeatability of the tests
Laboratory tests may be ordered at both the preliminary (fact-finding) stage and during court hearing.
Analyses ordered during the fact-finding stage are generally ordered by the Public Prosecutor but are sometimes requested by the defence lawyers during their own investigations.
Reports by expert witnesses, ordered by the Public Prosecutor, are governed by articles 359-360 of the Italian Criminal Procedure Code.
Art. 359 governs all investigations that can be repeated; this implies that biological traces can be analysed at least a second time. For this reason, the Public Prosecutor is not required to inform the parties, who are therefore unaware of the technical investigation conducted by the Public Prosecutor and thus cannot appoint expert examiners of their own (art. 360 of the Italian Penal Procedure Code). The repeatability of the tests means that the defence, in case of dispute, may have a new analysis carried out.
However, cases in which the test can be repeated are fairly rare. Consequently, investigations are almost always ordered as of art. 360 of the Italian Penal Procedure Code. Genetic-forensic analyses are indeed more often than not unrepeatable, whether for the limited quantities of traces available, for the poor quality of the DNA they contain, or for a combination of the two. In this case the Public Prosecutor is required to inform all parties (e.g. the defence lawyers for the victim and those for the person under investigation), so that they can appoint their own experts.
During the court hearing the Judge can order a report by an expert witness. This is governed by art. 220 and those following of the Italian Penal Procedure Code.
Both in the case of an expert examination ordered by the Public Prosecutor and in that of a report by an expert witness ordered by the Judge, the expert is chosen from specific professional registers divided into categories of experts.
Interpretation of the data
A laboratory analysis produces data that must be interpreted by the operator.
Interpretation is a critical reading of the result and its incorporation in a more general context. The interpretation is easy when the results of the analysis are completely clear, like a photograph taken in good light which shows details that are evident to all and cannot be disputed. If the photograph is blurred or taken on a rainy day, then many details may fail to emerge or may be subject to different interpretations.
In these cases, the operator's experience – and often their prudence – are fundamental.
The myth of the infallibility of the DNA test as a cure for all legal identification ills indeed needs to be taken with a pinch of salt. All too often the limited quantity, or poor quality, of the DNA available does not allow a univocal interpretation. Hence the heated debates between expert witnesses of the prosecution and the defence which we have seen in so many recent court proceedings.
From:
Cazzaniga, Cattabeni, Luvoni, Zoja.
Compendio di Medicina Legale e delle Assicurazioni.
UTET Giuridica, 2022
Book chapter by A. Piccinini (mod.).
