A 60-year-old woman arrested on suspicion of manslaughter after three people died at a Swanage care home has been released without charge.
Police said the deaths of the Gainsborough Care Home residents – two men aged 74 and 91 and an 86-year-old woman – are still being treated as unexplained.
They previously said carbon monoxide poisoning was the main line of inquiry.
Seven people were also taken to hospital and the property was evacuated following last month’s incident.
Detective Chief Inspector Neil Third said Dorset Police were working with the coroner to try to establish a cause of death.
He said the woman had been arrested “to take a full account and recover any available evidence, while providing legal protection to the person”.
DCI Third said they no longer believe she was responsible for any “actions or omissions” that were grossly negligent.
He added: “Our investigation is very much still ongoing and we are awaiting results from detailed forensic submissions and analysis to assist us in establishing the causes of the deaths, which may take several months.
“The families of the residents who sadly died are being kept informed with any updates in the investigation.”
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The care home, run by Agincare, has 48 residents, all elderly and some with dementia.
All residents were evacuated to a nearby church hall after the emergency, which started around 5am on 23 October.
A hazard response team, 10 ambulances and six fire crews were dispatched and gas engineers were also later on site.