A teenager stabbed a neighbour to death after seeing the man fatally stab his mother at their home in Hertfordshire, a double inquest has heard.
The hearing has been told James Killen, 18, was getting ready for school in St Albans on 30 April when he heard his mother Sandra Crawford, 53, scream.
He found Ms Crawford being stabbed by next-door neighbour Jonathan London.
Mr Killen punched Mr London, 47, and then got a knife and stabbed him 16 times, the inquest heard.
Mr London died at the scene from a punctured lung while Ms Crawford, who staggered on to the front lawn, died in hospital eight days later from chest and neck injuries.
'Worst' delusional case
In the months leading up to the incident, Mr London had been complaining of hearing noises in his head and on 29 April was taken to hospital by his family.
He was given a blood test and sent home, the inquest heard.
Psychiatric nurse Jocelyn Cusack, who saw Mr London that day, said he was delusional and it was one of the worst cases she had seen in 20 years.
Psychiatrist Dr Seshni Moodliar said she felt he did not pose a threat to himself or others.
A mental health team was due to see him at home at 1130 BST on 30 April, but at 0830 BST he left the house he shared with his elderly parents in Sherwood Avenue and attacked Ms Crawford.
Scream of 'die'
Police officer Claire Moy, who attended the scene, told the inquest Mr Killen was "shaking uncontrollably" and kept asking after his mother.
Describing what Mr Killen had told her, she said: "He saw a man punching her (Ms Crawford) and screaming 'die, die'."
The hearing was told he punched Mr London, which had no effect, so he got a knife and stabbed him "a few times".
Mr Killen was arrested but no charges were brought against him.
Coroner Edward Thomas expressed his sympathies to both families and gave a narrative verdict that Sandra Crawford died from stab wounds inflicted by a person suffering a severe mental illness.
He recorded Jonathan London's death as a lawful killing.
Mr Thomas said he was satisfied Mr London suffered from a major mental illness.
There was no previous psychiatric history and he could understand why it was felt he would be assessed for home treatment and remain in the community.