The scientific evidence reveals that a child/young person with developmental delays will lack legally relevant capacities similar to the abnormal developing child, such as defective risk assessment, distorted temporal perspectives and impulsivity. Although, they suffer a higher degree of developmental immaturity than the norm for a person their age, cognitive impairment and might lack legally relevant capacities. The problem is that their degree of incapacity is not significant enough to warrant a diagnosis of “a recognised medical condition” under Section 52 of the Coroners and Justice Act 2009. This means they cannot successfully plead the defence of diminished responsibility if they kill because they cannot prove they suffer an “abnormality of mental functioning” arising from “a recognised medical condition.” In this paper, I argue that the Government wrongly anticipated that there would be interpretational flexibility with “a recognised medical condition” under Section 52 for juveniles. Developmental immaturity is not accepted as a medical disorder, illness, or condition; thus, these persons who kill and lack legally relevant capacities fall outside the remit of the defence and are convicted of murder.

The Law Commission subsequently considered whether a new complete defence of “not criminally responsible because of developmental immaturity” should be introduced for those who kill under 18 years of age. The scientific evidence suggests that a developmentally immature child/young person typically suffers diminished capacities, not a complete loss of capacity. Thus, they would still be convicted of murder if this defence were to be introduced.