After a 25-year-old woman goes missing in Bristol, the police launch a major missing-person enquiry. Soon after, the body of the young woman is discoved by dog walkers on Christmas Day, and the hunt becomes a major murder enquiry. As investigators can find no sign of forced entry to her flat, they conclude that her killer must be someone known to her.The investigating officers initially hope DNA evidence would lead them to her killer, but when this evidence fails to reveal any further leads, they turn to Kelly Sheridan, an expert in fibre analysis. Her first priority is to see if there are any foreign fibres on the victim's clothes. The evidence she finds proves crucial in identifying and convicting the killer, who is not who the police thought.In Wales, we discover how the analysis of mobile phone data helped convict the men behind a brutal murder. Initially, the police thought they were investigating a violent burglary, but following the death of a young man, their investigation immediately turned into a murder inquiry. Expert witness Paul Hope then found texts on a phone that put friends of the victim in the frame.