Statistical evidence and DNA in the criminal procedure

Judicial statistics is generally referred to as the detection of data on crimes and trial outcomes, with subsequent analysis of the data thus detected. Statistics applied to the evaluation of evidence is increasingly being recognized as an important part of the modern criminal justice system. This paper is about the use of DNA test for identification and judicial purposes – the greatest revolution in criminal investigation –, also in reference to a concrete case of statistics applied to forensic genetics. Forensic science is the application of scientific methodologies to traditional investigative techniques in relation to the detection of a crime: its scope is wide, ranging from biology to psychology, chemistry, computer science, physics, medicine and engineering. Forensic genetics is a specialized branch of forensic science, which analyzes the DNA to prove suspicious responsibility for a crime. Science and law walk together in the process of determining the procedural truth, from the preliminary investigation phase to the final judgement. Statistical evidence is not always considered reliable in the criminal procedure, as it is based on a subjective probability concept. On the other hand, a rational evidence that can claim criminal liability “beyond any reasonable doubt” is necessary. In this regard, in this paper we analyze how the DNA test can be considered a scientific, reliable and valid evidence when contextualized and evaluated together with the other elements found during the criminal procedure: scientific investigation and traditional investigation tools must go hand in hand towards determining the procedural truth. The scientificity of identifying the individual by typing the DNA profile detected on the crime scene is thus validated, until constituting scientific evidence in the criminal procedure, supported by the statistical calculation of the rarity of the probability that the typed genetic profile could be casually attributed to another individual in the world population.