One Trace, Several Readings: A Way to Tell How Firm a DNA or Fingerprint Result Is, Using the Laboratory's Own Settings

A crime-scene trace is recorded once, either a DNA profile or a photographed fingerprint, and a computer program then gives one result from one set of processing settings. This concept note describes a simple check for police and forensic laboratories. From the record the laboratory already holds, the computer makes two to four versions by changing only the laboratory's own processing settings, inside the range the laboratory has already validated. The same program reads every version unchanged. If the results stay together, the result is firm. If they spread out, the result depends on a setting. One number, the spread value, shows which case it is. A computer-decided shunting action then moves the case that needs care to the front of the senior examiner's list while all other cases carry on. The check never picks a version and never changes the reported result. It adds no new test on the sample, and the decision stays with the examiner. The note covers fingerprints and DNA, compares the approach with earlier published work and patents, and explains how it differs. Keywords: forensic DNA, fingerprints, likelihood ratio, probabilistic genotyping, latent prints, stability, early warning, shunting action, police laboratories