How does psychological profiling work? How can science detect art fakes and forgeries? The 'Why Science Matters' series demonstrates how the science we learn at school is important in every aspect of our everyday lives. Using case studies and investigations, the series describes the development of science and technologies that can improve our lives – or lead to new scientific challenges and controversies. In 'Fighting Crime', we find out science can transform the chaotic jumble of specks, smudges, splinters, and stains at a crime scene into the story of the crime and the identity of the criminal. We learn about the careful analysis of evidence, such as DNA and fibers, the chemistry of catalysts, fires, and explosions, and how forensic scientists can accurately determine the time of death of a murder victim.