. >> reporter: david leban is a former gang prosecutor.the ceo of the association of prosecuting attorneys. >> on behalf of prosecutors, if it's matching, that would very much be another piece of evidence that we would like to admit in the case because we think it is relevant. >> i can tell you that it's in the hundreds. >> hundreds of instances? >> hundreds of instances where rap lyrics are being used at some point in the criminal justice process. >> eric nielsen of the university of richmond is a scholar of rap and a strong critic of its use in criminal proceedings. he says it too often mistakes a musical art form for evidence of criminal behavior. >> i mean, what prosecutors have found is that when they could introduce rap lyrics as evidence, particularly in situations where they don't have strong evidence otherotherwise, are still able to secure convictions. >> no one tracks exactly how often rap here rick used to secure convictions in court. just as know one keeps track of how often they're used to secure plea bargains before trial. t