A woman was found collapsed in the garden of a residential property and pronounced dead at the scene. She had been beheaded with a machete. The victim was later named as 82-year-old Palmira Silva and her family informed.
The suspect also "decapitated two cats in a quiet London street" before the attack, the Mirror reported.
Early reports that the murder was not a terrorist event were correct but in light of recent beheadings in Iraq people were obviously jittery that it was terrorist related. 25-year-old Nicholas Salvador was arrested at the scene.
The court heard that in his demented state Salvador believed the cats were demons and that Ms Silva was also some sort of demon or supernatural entity possibly Hitler back from the dead.
His plea in court Monday, accepted by both the defence and prosecution teams, is not guilty by reason of insanity.
Salvador had killed two cats when he came across Ms Silva in her back garden. He was on the rampage and people were hiding in doors; police were responding to the events and a police helicopter was flying overhead. He vaulted Silva's fence and hit her with a pole before stabbing her in the back more than once. He then severed her head and held it up for those in the helicopter above to see.
Initially police did not confirm the cause of death but there were already some reports that said the victim was hacked to death with a machete. Early BBC reports said "Police said the woman's next of kin had not been informed so they were unwilling to speculate on the nature of the woman's injuries or the type of weapon used".
One attending police officer reportedly suffered a broken wrist at the scene.
Terrified residents were told by police to leave their properties as armed police responded. Children were playing in the area but police managed to warn them to get away.
Police officers were carrying Tasers which were used half a dozen times on the frenzied suspect. "In police commentary, an officer could be heard to say: "He's agitated and lethal ... he needs taking out" reports Sky News.
The accused was seen fighting with police and according to the Independent on the day of the killing; DCI John Sandlin, leading this investigation, said: "This is was a highly visible attack in broad daylight on a residential street. I can understand why this may cause people concern, however we are confident that we are not looking for anyone else at this stage. "Whilst it is too early to speculate on what the motive behind this attack was I am confident, based on the information currently available to me that it is not terrorist related."
The court proceedings are expected to be brief. Consultant forensic psychiatrist Dr Frank Farnham is convinced Salvador suffers from paranoid schizophrenia, adding its chief symptom was a "loss of contact with reality". Another health professional described Salvador as a gentle giant claiming he was not violent before his mental health breakdown.
Salvador has been assessed as being as 'mentally troubled as it gets' and needing several years of treatment.
But news that he may be released back into the community at some point in the future has to be a worry.
Sarah Hajibagheri from Twitter tweeted from the trial "After several yrs at Broadmoor, he would go to a medium security facility before potentially being released bk into community&meds monitored."
Mrs Silva moved from Italy to the UK in 1953, had two children and six grandchildren.
The trial is now adjourned until Tuesday.
Updates to follow as available