Isaac Oar was pronounced dead at an Alice Street address in Ayr, south of Townsville in north Queensland, on August 10, 2023.
Police have been investigating Mr Oar's care and treatment after his suspicious death 17 months ago and have made a renewed public appeal for information.
They are specifically asking members of the Burdekin community to come forward with information about his care or medical treatment.
"Isaac was found seriously malnourished - he was only 29 kilos at the time of his death," Detective Inspector Jason Shepherd told reporters on Thursday.
"He was being cared for by a family member.
"He hadn't been or received any professional medical treatment in well over a decade so it makes the investigation quite complex.
"We do believe people would have had contact with the family members, would have had contact with the house at times during the years preceding his death, and we believe that those people may be able to assist us."
Police allege Mr Oar's condition stemmed from years of neglect.
Det Insp Shepherd said Mr Oar's primary caregiver, his older sister, was a person of interest in their investigation.
There is no suggestion by AAP of any wrongdoing.
"At this stage, the primary person of interest is your primary carer," Det Insp Shepherd said.
"There's no other information to suggest that other people would have been involved in him leading to be in the state that he was found in."
If police did not find an offender responsible, the investigation would shift to the coroner and potentially a coronial inquest, Det Insp Shepherd said.
A funeral was held for Mr Oar at Ayr's Sacred Heart Catholic Church on August 24, 2023.
