Jiaxin Tu was capable of knowing right from wrong when he is said to have crept into his flatmate's bedroom and struck him on the head with a hammer as he slept, a psychiatrist has told the High Court in Auckland.
Mr Tu denies murdering 19-year-old Shane Paul Hawe-Wilson in July last year.
Psychiatrist Peter Dean told the court Mr Tu was influenced by his schizoaffective disorder at the time of the killing but not to the degree that he was legally insane.
Dr Dean said Mr Tu had previously believed he was God or Jesus and had a poor history of taking his medication.
He said his use of cannabis and alcohol also exacerbated his poor mental health.
A jury of eight women and four men is hearing evidence in the High Court from 38 witnesses.