"Killing another person is humanity's greatest taboo. Most of us, thankfully, will go through life without having taken someone else's. And it's precisely because I'll never know at first hand what it's like (I hope) that I'm so curious to get inside the mind of a killer. Whether it's someone who is sanctioned to kill, like a soldier; someone who kills accidentally, like a dangerous driver; or someone who does it on purpose, like a murderer, I want to know the answers to all sorts of fascinating questions. What goes through their mind at the time? How did it happen? How do they feel afterwards? And are they haunted by the event for the rest of their life?"

In this first programme she talks to Chantelle Taylor, an army medic who shot a Taliban fighter when caught in an ambush in Afghanistan.

Producer: Lucy Lunt.