Personality disorders, which may not be significant in themselves in reducing culpability, may nevertheless have an impact on sentence in explaining and therefore reducing the impact of other aggravating features.
Mr De Silva was convicted of murder and sentenced to life imprisonment with a minimum term of 32 years on 24th February 2014. The defendant had inflicted 22 individual stab wounds on his victim in the course of an aggravated burglary. He was 19 years old at the time of the commission of the offence, and 21 at the time of sentence.
While on remand for the murder, Mr De Silva was transferred from HMP Belmarsh to Broadmoor Hospital as a result of concerns for his mental state and fitness to plead. He was diagnosed with dissocial personality disorder, which resulted in symptoms such as callous unconcern for the feelings of others, disregard for social norms and low threshold for discharge of aggression. Despite this, he was found fit to plead and capable of forming the relevant criminal intent; none of the psychiatrists that examined him found a mental disorder that substantially impaired his ability to form a rational judgment or exercise self-control.
In sentencing, the judge took account of the medical evidence, but was of the view that the defendant's culpability was not lowered by the fact that he suffered from a personality disorder, which he described as "a condition far from uncommon amongst those who commit murder."
Mr De Silva appealed against sentence on the ground that the minimum term of 32 years was excessive for a man who was 19 years of age at the time of the offence. Counsel for Mr De Silva referred to R v Peters and others  2 Cr App R S 101, that age and maturity are important factors when dealing with an offender under 21 at the time of their offences.
Counsel for the Crown submitted that youth of the defendant does not amount to significant mitigation where culpability remains high.
Further, there was an appeal on the basis that his personality disorder was significant, as was the fact that he had had a very troubled background, including being taken into care at the age of nine following severe domestic violence within the family.
Held: that the judge was correct in concluding that a personality disorder did not constitute any significant mitigation where the defendant remains capable of forming the requisite intent. However, whilst a personality disorder does not diminish an offender's culpability for his deliberate acts and use of deadly force, along with youth it may explain and reduce the impact of other aggravating features such as a long antecedent history.
Regarding youth, even where there is high culpability for the offence, age will be an important factor in mitigating culpability, on the grounds that young offenders are more likely to be "impulsive, unthinking, and respond to situations with excessive and gratuitous force." On this basis, the overall sentence was found to be too high and accordingly manifestly excessive.
The minimum term was quashed and substituted with a term of 28 years.
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