"Mr Acheson, a senior adviser with the US-based Counter-Extremism Project, said society must understand how terrorists are radicalised and motivated. 'We don’t want to in any way, shape or form cede any ground to people who wish to murder for ideological or theological reasons,' he said. 'But we can’t talk to dead terrorists. We can talk to the ones who are alive and in custody. We can learn so much from them. That includes people associated with extremist movements, people like Lisa Smith and others in Syria.'"