Stephen Bouquet, 55, a former security guard, died in Medway Maritime Hospital on January 5 last year.
Bouquet was jailed for five years and three months in 2021 for his cat-killing spree in East Sussex.
At an inquest held in Maidstone, Kent, coroner Patricia Harding ruled Bouquet’s death as natural causes, with the medical cause of death confirmed as Covid-19 pneumonitis, and a secondary cause of chronic obstructive pulmonary disease.
He was also receiving end-of-life care for thyroid cancer while serving his sentence in HMP Elmley.
The coroner said it was ‘not clear’ where Bouquet contracted coronavirus, either in hospital or in prison, but he tested positive for the illness on December 28, a day after he was admitted to Medway Maritime Hospital for a cough and difficulty breathing.
Despite receiving antibiotics, oxygen and medication specifically to treat coronavirus, his condition ‘progressively deteriorated’, the inquest heard.
Ms Harding said: ‘Despite whatever measures, he was too weak to fight the infection and sadly he died on January 5 2022, on his 55th birthday.’
The coroner also noted that earlier in December when Bouquet was transferred to HMP Elmley, he was ‘extremely frail’, had poor mobility and was ‘vulnerable to infection’.
But Ms Harding also said she was ‘satisfied’ that the prison followed national guidance during the pandemic to minimise the spread of the global virus.
Bouquet was serving his five-year-sentence after being found guilty of 16 offences of criminal damage in relation to cats, as well as possession of a knife.
He carried out a string of attacks on pets in Brighton between October 2018 and May 2019, before being caught on CCTV set up by one of the victim’s owners.
Nine cats – Hendrix, Tommy, Hannah, Alan, Nancy, Gizmo, Kyo, Ollie and Cosmo – were killed, while another seven were injured.
Bouquet had previously served in the Royal Navy for 22 years, including in Northern Ireland and Iraq.
Addressing Bouquet’s brother at the inquest, Ms Harding gave her condolences and apologised for the length of time it has taken to reach an inquest conclusion.
She said: ‘Covid not only had an effect on everybody touched by it but also its lasting effects (mean) the investigation has taken a lot longer….I’m sorry it’s taken so long.’
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