Professor David Wilson, the UK's leading criminologist, presents the third series of Crime Files, this time focusing on cold cases. In episode 7, David retraces the last known steps of Glenrothes man Allan Bryant and asks ‘how does someone go missing without a trace in the digital age?'.Dr Kirsty Bennett from Leeds Beckett University has a special interest in missing people. She talks to David about her research into the methods of locating missing people as well as the missing continuum and the various reasons why people might disappear.David, this series, is joined in studio by our resident Forensic Scientist Helen Meadows. This week Helen talks to David about where to start when someone goes missing and how to build up a picture of their movements. She also looks at the murder of Louise Tiffney in 2002. Even though Louise had not been found she was presumed dead and her son faced trial. He was given a Not Proven verdict but when her body was eventually discovered in a shallow grave in 2017 new evidence provided further links to the crime.Professor Lorna Dawson, soil expert and head of forensics at the James Hutton Institute tells David how she was tasked with gathering soil evidence and carrying out analysis in order to bring the accused back to trial under the double jeopardy principle.