Forensic expertise and judicial practice: evidence or proof?

This study presents for discussion the possibility of adopting a hypothesis of absolute truth in forensic serology and DNA testing of biological traces, taking into account identification probability, which is usually assumed to be greater than 95%. Can this be so? Established identity and mathematically calculated probability below this rate is not false because it depends on the sensitivity of the method, the possible number of variations and theoretical combinations. The result from a study can be considered a 100% identification result only if this study takes account of absolutely all quantitative criteria that characterize it.

Under the conditions of continually evolving theory and practice, and the introduction of modified and expanded methods for analysis of biological materials, it may therefore be asked which method considers 'everything'. Although this finding is nihilistic, it reflects a truth, which we can define as absolute. In forensic practice, research methods assumed to be orientation ones and others identified as evidence for the presence of biological traces on objects carriers, are routinely employed.

Based on several groups of forensic cases, the question of the limits of precision and relevance of the results to the categories of evidence and proof is formulated and discussed. Three groups of expertise cases are presented, which warrant discussion: (i) a study of condoms with genetic material on both sides: female DNA on the outer surface and male DNA on the inner. What is this evidence for or what does it prove?; (ii) a study of cigarette butts found at a crime scene with deposited cellular material from the offender. Is this evidence or proof?; (iii) the DNA expertise in the case of controversial parental origin or the vasectomy of the man referred to as the father.

What will the court choose as proof or is it a case of mutually exclusive evidence? Such considerations lead to the dilemma: 'evidence or proof'?