Police have arrested a man at a home south of Wollongong after the body of his father was discovered on Sunday night.
A neighbour called police on Sunday afternoon after noticing the 74-year-old lying in the backyard of his Farmborough Heights home.
Paramedics attended the scene but found the man deceased with serious head injuries.
The man's 48-year-old son, who also lives at the address, was arrested by officers.
He was taken to Lake Illawarra Police Station where he was questioned by police.
Lake Illawarra Police Crime Manager, Detective Chief Inspector Brad Ainsworth, said it was a confronting scene for the quiet suburb.
"Obviously it is distressing and disturbing for the neighbours that found him and the police on the scene," he said.
"But I can assure the members of the public that it is safe in Farmborough heights — this is an isolated incident."
Chief Inspector Ainsworth said the man was "not extensively" known to police.
He said the 74-year-old was last seen on February 1 and police were still working to determine the exact time of death.
"There is a possibility he has been there for some time — whether that is one day or two days, we are not sure," Chief Inspector Ainsworth said.
Police have established strike force Oketo to investigate the circumstances surrounding the death.
Forensic officers have spent the morning gathering evidence at the home while detectives have interviewed neighbours.
A report will be prepared for the coroner.