A mentally ill man who started a fire in his grandmother’s home, leading to her death from inhalation of fumes, had not done anything like it before and it could not have been “second guessed”, a coroner has said.

Vera Croghan, 89, died as a result of inhaling fumes after Chanatorn Croghan – known as Marco – started a fire at her house in Norwich on December 11 2020.

He was sentenced at Norwich Crown Court in 2022 – at the age of 21 – to be detained in a mental health hospital after admitting manslaughter by diminished responsibility.

Norfolk area coroner Yvonne Blake concluded at an inquest in Norwich that Mrs Croghan was unlawfully killed and noted there had been an accepted plea of diminished responsibility for manslaughter.

Summing up evidence in the case, she said Mr Croghan’s father Richard had moved in with his mother, Mrs Croghan, to look after her in 2019.

The coroner said Mrs Croghan’s grandson had previously been admitted to a psychiatric unit in Thailand, where his mother lived, and had also been sectioned in England after a psychotic episode in May 2020 when he punched his father in the face.

She said he arrived at Mrs Croghan’s house “suddenly” on December 9 2020 from Manchester, where he had been at university.

In a Record of Inquest document, the coroner said he had stopped taking his antipsychotic medication when he went away to university and “he was not followed up there because he refused consent”.

Richard Croghan called police after he feared, late on December 10, that his son would become violent and said the younger man was staring at him “as if he was going to kill him”, the coroner said.

She said police attended and did not find any offences had been committed and that Marco Croghan was not acting in a way to cause them concern.

They did not believe he needed a Mental Health Act assessment, the coroner said in her Record of Inquest, with Mrs Croghan “apparently undisturbed”, although Richard Croghan “was not reassured and left the property intending to return in the morning to deal with” his son.

Richard Croghan left to stay at another address in Norwich with his partner and turned his phone off, the coroner said.

After a fire alarm was triggered at 4.40am on December 11, a passer-by dialled 999 and Mrs Croghan was found in her room directly above where the fire was lit under the stairs.

The coroner said there were fire detectors and smoke alarms, but Mrs Croghan had hearing loss.

Ms Blake said: “He (Marco Croghan) had never done anything like this before so I don’t know how anyone could have second guessed it really.”

She said his father “wouldn’t have left her (Mrs Croghan) if he thought she was in danger”.

Summing up Richard Croghan’s evidence, the coroner said: “He said he thought Vera would be safe when he left as Marco had shown no aggression to her.”

Ms Blake added: “Punching and throwing things might be what you might have expected but the fire starting was a complete surprise to me.”

She said the younger man declined to take part in the inquest proceedings and refused access to his medical records.

Mrs Croghan was a lecturer in Swedish and Scandinavian studies at the University of East Anglia before her retirement, and was the author of the best-selling Teach Yourself Swedish book.

Her daughter, Karin Ronen, who attended Tuesday’s inquest, said afterwards that there had been “no justice” and “so many questions remain in our opinion deliberately unanswered”.

“Mum was an elderly and gentle lady who had many vulnerabilities in her later years,” said the 63-year-old nurse.

“She had contributed to society her whole life and instilled in us a keen sense of independence and an understanding of right and wrong.

“She deserved dignity in death. Instead this final attempt to get some answers following the horrific death of our much-loved mum has left us feeling disappointed and frustrated with the system.”