In the early hours of a Tuesday morning in Birmingham, Pablo Hoad rings 999 to say he has killed his flatmate. He claims the victim, 27-year-old Shannon Stanley, went to stab him with a knife after an argument broke out between them and he killed her in self-defence. Police and forensic officers must determine if the victim was actually killed in cold blood, with forensic scientist Andrew Palmer carrying out blood-pattern analysis to attempt to map out the sequence of events surrounding the fight.