Britain’s longest serving murderer, John Massey spent 43 years in prison for the fatal shooting of a nightclub bouncer in 1975. Now aged 71, Massey submits himself to a ground-breaking biological and psychological investigation to determine whether he truly had control over his actions or if a combination of hidden factors made him destined to kill.

The second episode of this three-part series explores seemingly random murders at the hands of a stranger as neuro criminologist, Professor Adrian Raine and Forensic psychologist, Dr Vicky Thakordas Desai investigate the body and brain of convicted murderer Paul Aldridge.

In 1993 Anthony Powell, was a 21-year-old gang-affiliated enforcer in South London. Then one night, whilst collecting what he claims was a drug debt, he shot a man dead with a sawn-off shotgun. He was convicted of murder and served over 21 years in prison. Now, 7 years on from his release, Anthony submits himself to a ground-breaking biological and psychological investigation.