An investigation was launched following an incident on Boxing Day last year where five people were taken to hospital following the suspected gas leak at the Royal Hotel, Marine Road Central, Morecambe.
All those affected on that occasion were discharged but police inquiries established that in November last year a 66-year-old man had died at the hotel.
Tests showed Graham Holden, who was from Burnley, had a high level of carbon monoxide in his blood.
On Thursday, June 9th, two people were arrested on suspicion of manslaughter. They are a 41-year-old man from Morecambe and a 42-year-old man from Bolton le Sands.
On Friday. June 10th, a 66 year old man from Morecambe was arrested in connection with this investigation.
Last week two further people were interviewed in connection with this inquiry - a 72-year-old man from the Morecambe area and a 50 year old man from Morecambe.
A spokesman for the hotel, which is now under new management, said: "We took ownership of the property last month.
"We are aware of the situation with the previous owners and would like to state that procedures are in place to ensure the safety of all customers.
"Ours thought are with the family of Graham Holden at this difficult time."
Lancaster City Council, which conducted a joint investigation with police and the HSE into the incident on Boxing Day, declined to comment due to the ongoing police investigation.
DI Dylan Hrynkow, of West CID, said: “This is an incredibly complex and sensitive investigation and I would ask for patience while we establish the full circumstances of what has occurred.
"However, my thoughts are very much with the loved ones of the deceased at this time.”
The police investigation into the cause of the suspected carbon monoxide poisoning is continuing and anyone with information is asked to contact 101 quoting log reference 0353 of December 26.
Alternatively contact independent charity Crimestoppers on 0800 555 111.