 Consider a case in which a DNA match is the primary incriminating evidence. DNA evidence is one of the most widely used forms of quantitative evidence currently available, but it does not work much differently from blood evidence or other forms of trace evidence. In testifying about a DNA match, trial experts will often assess the probability that a random person, unrelated to the crime, would coincidentally match the crime stain profile (Foreman et al. 2003). This is called the Genotype Probability or Random Match Probability, which can be extremely low, in the order of 1 in 100 million or even lower (Donnelly 1995; Kaye and Sensabaugh 2011; Wasserman 2002). It is tempting to equate the random match probability to \(\Pr(\match \pmid \textsf{innocence})\) and together with the prior \(\Pr(\textsf{innocence})\) use Bayes’ theorem to calculate the posterior probability of innocence \(\Pr(\textsf{innocence} \pmid \match)\). This would be a mistake. Applying Bayes’ theorem is of course recommended and helps to avoid the prosecutor’s fallacy, the conflation of \(\Pr(\textsf{innocence} \pmid \match)\) and \(\Pr(\match \pmid \textsf{innocence})\). The problem here lies elsewhere. Equating the random match probability with \(\Pr(\match \pmid \textsf{innocence})\) overlooks the difference between offense, activity and source level hypotheses. A DNA match cannot speak directly to the question of guilt or innocence. Even if the suspect is the source of the genetic material at the scene, the match does not establish that the defendant did visit the scene and came into contact with the victim, and even if they did, it does not follow that they committed the crime they were accused of.