Blood and fibres are often collected at a crime scene and used as evidence to track down the perpetrator, so forensic science makes an ideal context to present lessons on these topics.  Whilst solving a mystery, students can gain experience with microscopes, understand the need for experimental controls and learn about the composition of blood, and the structure and properties of fibres.  Participants will use luminol to find traces of blood then carry out an ABO blood typing exercise on realistic artificial blood.  To complete the workshop, various natural and synthetic fibres will be examined to determine their source.  Can we identify the guilty party?