In every murder investigation, there's one key item that could bring a killer to justice. But finding it....and knowing what evidence it contains....well that's the challenge. Because the smoking gun could be anything. A bouquet of flowers...a Chinese meal...a mosquito. In this series we tell the remarkable true stories of how everyday items such as these have been the key to unlocking a criminal case. And we unpack the science - revealing the cutting edge techniques and the disciplines mastered over decades, which allow specialist forensic scientists to find this evidence. Hosted by actor Romola Garai, and the UK's most prominent forensic scientist Tracy Alexander.