Detectives are trying to work out how a popular and well-known member of an Upper Hunter community died from a "highly dangerous poison" that is sometimes used to kill vermin and wild dogs.
Emergency crews found Douglas Thrift dead in his home on a property at Denman on the night of December 1, 2018, only a few hours after he finished a round of golf.
Police are treating the 71-year-old's death as suspicious - they say they have been doing so "since day one".
But police would not be drawn on Tuesday as to whether detectives believed he had been murdered, with one senior investigator saying police were "keeping an open mind".
Detective Inspector Matthew Zimmer told reporters in Muswellbrook that expert medical evidence clearly showed Mr Thrift died from a fatal concentration of the "highly toxic" substance strychnine.
"Unfortunately, Mr Thrift would have suffered quite an horrific death," Inspector Zimmer said.
"We are very interested in speaking with people who may have had conversations with him in the days and hours prior to his death."
Inspector Zimmer said Mr Thrift was a "loving father and grandfather" who had strong ties to the community - particularly in local sports.
"We have no information to suggest Doug had any enemies - he was a very well respected member of the Denman community," he said.
"He was actively involved in the sporting community, he was an avid rugby player, he was into his cricket and he loved his golf and he was most happy on his farm."
In a tribute piece published soon after Mr Thrift died, the Singleton Argus noted the Hunter man was part of the Singleton Bulls Rugby Club's inaugural match in 1967 and went on to play 117 grade games for the club, winning five premierships.
He was also part of the Singleton Greyhounds' Group 21 rugby league premiership side in 1974 and played representative cricket.
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The Newcastle Herald understands a family member made a concern-for-welfare call the night he died.
But when emergency crews arrived at the home where Mr Thrift and his wife lived, at about 8pm, the 71-year-old could not be revived.
Inspector Zimmer said the evidence suggested the poison had been ingested and police wanted to figure out how this had occurred.
Mr Thrift had received the all-clear following a previous cancer diagnosis and police understand the Hunter man had been making plans - at least some of them long-term - in the days before his death.
"We have information to indicate that Mr Thrift was in good spirits the day he passed away," Inspector Zimmer said.
"The family wants some answers."
When asked whether police had identified any persons of interest, Inspector Zimmer said investigators were continuing to follow "all lines of enquiry".
Strychnine is a restricted material that the NSW government has classified as a "highly dangerous" Schedule 7 substance, alongside arsenic, cyanides and thallium.
"The acquisition or use of any of the above substances without an authority issued by the Ministry of Health is an offence, as is their supply, unless the person being supplied holds an authority to use the substance," according to a NSW Health information brochure published last year.
Strychnine is sometimes used by property owners in rural areas to kill vermin and troublesome wild dogs in order to protect crops and livestock.
Investigators are interested in hearing from people who had strychnine go missing from their properties in the lead-up to December 1, 2018.
Police are urging anyone with information that could help investigators in the matter of Mr Thrift's death to contact Crime Stoppers on 1800 333 000. Information can be given to police anonymously using the Crime Stoppers hotline.
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