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....