Inside the mind of a forensic botanist, Mark Spencer tells Jim Al-Khalili how he uses plant evidence to help solve crimes. By studying the vegetation at crime scenes, Mark can tell how long a dead body has been laying in the ground. Brambles can be particularly informative, he says. And by looking at tiny traces of plants under the microscope, he can link suspects to victims, or particular locations. Mark tells Jim Al-Khalili how he came to be a forensic botanist. After working in bars and clubs in Soho for many years, he decided to study for a degree in botany and developed a special interest in water moulds. As a curator of the botanical collections at the Natural History Museum in London, he became intimately acquainted with British flora past and present. And, more recently, has spent a lot of time monitoring urban wildlife – recording how the composition of native species and non-native species in the capital is changing, as the global climate changes and the global trade in plants continues. Producer: Anna Buckley