John Charles Barrett had changed his will just hours before he died, an inquest has heard.
Police divers found the 90-year-old's body at Hully Farm, Tybroughton, near Whitchurch on the Shropshire/Wales border, on January 2, 2020 - the day he visited a solicitor to revoke and change his will.
The mobility scooter that belonged to Mr Barrett, who was known as Charlie, was found close to the lagoon.
During a pre-inquest hearing at Ruthin Coroner's Court on Friday, John Gittins, senior coroner for North Wales East and Central, said that while it was not his aim to “put dirty washing in public” he had to consider some of the background to Mr Barrett’s death.
“On that day he went to a solicitor and changed a will,” he said.
“He then returned home and is found in the slurry pit. That is where rumours and speculation come into play.”
Barrister Joseph Hart, representing the Barrett family, said: “The family are entirely aware of the fact there may be difficult questions.”
Mr Gittins said that at a previous pre-hearing Mr Hart had told the court he might be asking for a conclusion of unlawful killing to be considered.
Asked if that was still the case, Mr Hart replied: “Yes sir.”
When the inquest into Mr Barrett's death was opened in January 2020, the coroner was told that Mr Barrett was last seen at 6.25pm on January 2.
Later that evening a former employee of his became concerned when he saw there was no light on at his the house, before finding the mobility scooter near the slurry pit.
Emergency services were called and a specialist underwater search team found Mr Barnett, fully submerged in the lagoon.
After a post-mortem examination Home Office pathologist Dr Jonathan Metcalf gave a provisional cause of death as “immersion in slurry”.
Speaking on Friday the coroner said there was no doubt that Mr Barrett had the capacity to make any decisions but he would need to consider his mood and demeanour on the day of his death.
Mr Gittins said he would visit Hully Farm before the full inquest hearing on December 1. Mr Hart said that the slurry lagoon had been fenced off since the tragedy.