Echoes: One climber's hard road to freedom

'As I sat cradling the man's head, with his blood and brains sticking to my hands, I heard a voice – my own voice. It was asking me something. Asking how I had ended up like this, desperate and lost among people who thought nothing of caving in a man's head and then standing back to watch him die.'

Nick Bullock was a prison officer working in a maximum-security jail with some of Britain's most notorious criminals. Trapped in a...