A Royal Commission of Inquiry into mental health care is looking unlikely - despite pressure over repeat killings by two patients.

Hillmorton Hospital resident, Elliot Cameron, murdered his 83-year-old Christchurch gardening client in October, with new revelations he killed his brother 50 years ago.

This year, another man was found not guilty on insanity grounds - for killing a second time. 

Minister Matt Doocey says questions are being asked on clinical decisions. 

Doocey says he expects the external reviews and coronial inquests to be answering these questions, as that's why they take place. 

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