The final lecture in the series begins with a "heist". A jewel thief steals a precious man-made diamond from the Royal Institution’s collection. Can forensic evidence conclusively identify and convict the criminal responsible? To find out, the Royal Institution’s lecture theatre is transformed into a courtroom and the audience acts as jury on the case, with a special guest king’s counsel invited to defend the suspect. Forensic evidence is based on probability; it can never be 100 per cent certain. So, how convincing does the evidence need to be for the court of the Royal Institution’s own jury to reach a guilty verdict? Includes insights from real criminal investigations.