Shared psychotic disorder and the killing of a policeman: Barbieri v R [2016] NSWCCA 295

By December 2012, 19-year-old Mitchell Barbieri had adopted the persecutory delusions of his mother when he stabbed to death a police officer. Initially, both mother and son were charged with murder. After declining to accept his plea of guilty to manslaughter on the basis of ‘substantial impairment’, the prosecution offered the concession that Barbieri had a ‘significant cognitive impairment’ and that the usual mandatory life sentence for killing a policeman did not apply. Subsequently, both Barbieri and his mother pleaded guilty to a number of serious offences and were sentenced to quite disparate terms of imprisonment. The commentary examines the unique cases of a mother and son who had a shared psychotic disorder and whose charges arose from the same facts and circumstances but whose convictions attracted markedly dissimilar sentences. The relevant sentencing principles derived from recent case authority are considered and the reasoning of the sentencing judge is contrasted with the reasoning of the NSW Court of Appeal, which allowed an appeal from Mr Barbieri's original sentence.