MR JUSTICE Green sentenced Daniel Johnson to life behind bars and said he must serve at least 20 years before being even considered for parole.
The judge said the now double killer poses a “potentially lethal” threat to society, which cannot tolerate the risk of him taking a third life.
Johnson appeared in court via video link to Rampton high security hospital but will now be transferred into the prison system to serve his sentence.
Johnson believed “ray of sunshine” Gemma Finnigan, 24, had been possessed by Satan when he strangled and stabbed her 12 times at their home in Boldon Colliery last September.
The judge told him: “You have now caused two deaths.
“In my view your pattern of behaviour over the years exhibits a clear-cut propensity to extreme violence.
“It has not been suggested that the violence you committed when you were 15 was due to any mental illness.
“When that history is coupled to the present killing, I am left with the clear picture of a person who has it within him to commit terrible acts of wanton violence and that the inherent risk that you pose to society is increased by the fact you are prone to bouts of mental illness which have the effect of making you delusional and heedless and oblivious to the horrors of your own actions.
“Although I am told by the experts that you are no longer delusional or psychotic, none of them can predict if and when another equivalent episode might arise.
“in the past 15 years you have left in your wake two different, distraught groups of families and friends of people you have killed.
“So far as Gemma was concerned, I have heard that she was a vibrant and hard working young woman who was loyal and very close to her family.
“She had much to live for.
“She had a loving and close family who have been devastated by her death and by their loss of her.
“In my view you pose an extremely serious and potentially lethal threat to society and a threat that is not possible to say will necessarily will ever go away.
“You have now committed two acts of extreme violence over a period of 16 years. It might well be the case that you are today not suffering from any psychotic condition.
“However, no one can say if and when such a condition will return.
“I must take into account that society cannot tolerate the risk of a third death of an innocent person at your hands.”
Experts agreed Johnson was psychotic and delusional when he killed Miss Finnigan and is likely to have paranoid schizophrenia.
It remains unclear what extent his illegal drug use, of cannabis and opiates, had on his mental state.
The judge added: “The explanation you have subsequently given to the psychiatrists for your conduct is that on the night you though that Gemma had been possessed by some sort of a devil or a malign spirit and that it was using her to attack you.
“You believed that if you killed the body that was next to you on the bed you would save both Gemma and yourself.
“Evidence has been given to this court as to the extent of your abnormal conduct during that period and I accept the evidence of the psychiatrists that at the time you were suffering from an abnormality of mind that flowed from a recognised medical condition and which was in some substantial measure the cause of your conduct.
“This was not, however, your first killing.”