In our first story, a community reels in total shock when a doting grandmother is found murdered in her home. Detectives search for the killer and suspect it may be someone close to her. The suspect's DNA is found all over the crime scene, but that is easily explained because he lived until recently in the same house. So the police try another route. They approach Kelly Sheridan, an expert witness in fibre evidence, who uncovers a trail of fibres, unravelling the mystery and putting the killer in jail.More than 40 years ago, fibre analysis was still a relatively new forensic discipline. Despite this, police hoped it could help solve a string of child murders in the 1980s and 90s, but in the end it took old-fashioned detective work to close the case of killer Robert Black. Looking back, the case shows how this area of forensic science has been transformed over just four decades. Jim Fraser was the lead scientist in the Black investigation, and his experience shows that scientific progress is achieved through failure as well as success.