A man accused of beheading a pensioner in London believed he was killing "Hitler back from the dead" at the time, a court heard.
Prosecutors said a bare-chested Nicholas Salvador held Palmira Silva's severed head and showed it to a police helicopter hovering above the back garden where the 82-year-old was murdered last September.
The jury at the Old Bailey were told the 25-year-old went on a 45-minute rampage in Edmonton, north London, armed with a machete and a wooden pole.
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Salvador was a lodger at a house three doors away from Mrs Silva, and allegedly killed two cats before attacking her because he thought they were "demons".
He had smashed his way through garden fences and was just metres away from a group of playing children at one point.
One police officer climbed onto a nearby roof so he could warn them to seek refuge.
On the first day of his trial in central London, prosecutors said there was no dispute that the heavily-built defendant had killed Mrs Silva in her back garden.
Her family was clearly emotional as prosecutors explained how a post-mortem concluded she had sustained multiple, severe stab wounds to the upper-left shoulder and back.
Edited footage from the police helicopter, which omitted Mrs Silva's murder, was also shown in the courtroom - and featured Salvador talking to the victim while holding two weapons.
Salvador has pleaded not guilty "by reason of insanity", and consultant forensic psychiatrist Dr Frank Farnham said he had "no doubt" the defendant suffered from paranoid schizophrenia, adding its chief symptom was a "loss of contact with reality".
"I'm as clear as it can be, I have no doubt of his diagnosis," he said.
The court heard Salvador told the psychiatrist he thought Silva was Nazi leader Adolf Hitler in shape-shifted.
Dr Farnham said it was a "classic example of delusional misidentification syndrome",
Armed officers only managed to arrest him in the front room of another house on Nightingale Road in Edmonton after "a violent and chaotic struggle", which saw Salvador tasered six times.
One policeman, PC Bernard Hamilton, sustained leg injuries during Salvador's arrest and needed hospital treatment.
The court also heard how Salvador had shown signs of "odd behaviour" in the weeks before the beheading, repeating phrases such as "I am the King" and "red is the colour".
This "strange behaviour" had led to Salvador, who regularly smoked skunk cannabis, losing his job in billboard advertising three days before the great-grandmother's death.
