Nicholas Salvador, 25, had already beheaded two cats and was searching neighbouring gardens for more to kill, believing them to be “demons”, when he came across 82-year-old Palmira Silva, the court heard.
In his demented state, the paranoid schizophrenic killed Mrs Silva, believing she was a supernatural entity – either Hitler back from the dead or a demon in the guise of a little old lady, jurors were told.
Before the killing in September last year, Salvador had been staying with friends three doors away from Mrs Silva in Edmonton, north London.
At 1pm, he armed himself with the large knife and a wooden pole from the house. He killed the two family pets before making his way through a few back gardens.
He smashed his way into a neighbouring house and attacked a car containing two members of the family with whom he was living.
Salvador then went back through the house and into an alleyway that ran alongside Mrs Silva’s home where he came across the victim, jurors were told.
Video footage taken from a police helicopter overhead showed Mrs Silva, wearing a pinny over a dark skirt and white blouse, approaching the bare-chested Salvador over her garden wall.
After a brief exchange, Salvador vaulted into her well-tended flowerbed and stabbed her repeatedly before cutting her head off, the court heard.
The final moments of Mrs Silva’s life and the immediate aftermath were edited out of the harrowing 14-minute clip shown at the Old Bailey in front of a jury and members of the victim’s family.
Afterwards, the images showed Salvador tearing down garden fences and striding, still armed, within metres of playing children who were hastily evacuated out of harm’s way.
In police commentary, an officer could be heard to say: “He’s agitated and lethal . . . he needs taking out.”
Salvador was slippery with blood and sweat when he was eventually apprehended by armed police officers, after breaking into another neighbouring house. The officers were forced to Taser him six times.
His arrest was described by prosecutor Jonathan Rees QC as “violent and chaotic” and involved Salvador, who is heavily built and about 6ft, being kicked and punched to little effect.
In the struggle, one of the officers, PC Bernard Hamilton, received a leg injury which needed hospital treatment.
Meanwhile, Salvador was exhibiting signs of mental illness, repeating phrases like “Red is the colour” and “I am the king” over and over again. After being charged with Italian-born Mrs Silva’s murder, Salvador was remanded in custody at Belmarsh prison but due to his mental state was moved to high-security Broadmoor hospital.
In the weeks before, Salvador had shown signs of “odd behaviour” and had developed an interest in “shapeshifters” – supernatural entities that are supposed to physically transform into another being or form.
The skunk cannabis smoker had lost his job in billboard advertising three days before the killing over concern for his behaviour.
Salvador denies murder, by reason of insanity, and Mr Rees said that two psychiatrists would give evidence that he was suffering from paranoid schizo-phrenia.
Mrs Silva came to Britain from Italy in 1953.