Mr Joseph stabbed his field worker, Jenny Morrison, 127 times in an attack last November at the south London hostel where he was staying. The 50-year-old social worker tried desperately to fend him off but died before police and paramedics could get to her.
Yesterday psychiatrists at the Old Bailey trial debated whether Mr Joseph knew he was breaking the law when he killed Ms Morrison.
The court has been told that he believed he was acting under the orders of his "father, God". During an interview with Dr Paul Chesterman, a consultant forensic psychiatrist called by the prosecution, Mr Joseph said he had tricked Ms Morrison after she went to his halfway hostel in Tooting to tell him he had to return to hospital because he was not taking his medication.
He told her he wanted to go to the lavatory, but instead went to fetch a knife from the kitchen, Dr Chesterman said. He did not want to return to Springfield Psychiatric Hospital, Tooting, with the social worker because he was convinced he would be tortured there.
Dr Chesterman argued that Mr Joseph, now 27, knew what he was doing despite his severe delusions. Immediately after the killing, he had returned to his room, insisting that he had a machine-gun.
"It implies an awareness by Mr Joseph of the need to protect himself from others, most probably the police," said Dr Chesterman.
Despite the obvious bloody evidence, he went on to deny that he had stabbed anyone. The psychiatrist said: "The most logical explanation was his awareness that it was not appropriate to disclose to others what he had done."
Dr Chesterman said he could not be sure whether Mr Joseph's drug abuse had contributed to the killing. But he added: "It is certainly an important background issue to consider. There is evidence that people who suffer from schizophrenia exhibit violence after they've had a history of abuse of alcohol and illicit drugs."
He further argued that, of all the forms of schizophrenia, the paranoid type from which Mr Joseph suffered was least likely to impair his reasoning - a point over the which the defence argued.
Mr Joseph, a care in the community patient, killed the social worker five months after being transferred to the hostel from hospital.
Dr Chesterman said Mr Joseph still believed he was the son of God despite being treated with anti-psychotic drugs at Broadmoor special hospital. "Whatever the verdict [of the court], he will be in a secure hospital for the foreseeable future," the psychiatrist said, adding that Mr Joseph's general behaviour was "unremarkable" despite the persistence of delusions.
The jury will be asked on Monday to decide whether Mr Joseph is guilty of murder. He denies the charge on the ground of insanity according to the 147-year-old legal definition. He may still face a charge of manslaughter on the ground of diminished responsibility.Reuse content