Guy Haymes was discovered with serious head injuries in a unit at Manly, on the city's northern beaches, on the evening of February 27.
The 59-year-old, known as "Creature" to his friends, was taken to Royal North Shore Hospital with critical head injuries after the suspected assault, but died on March 15.
Detectives have spent three months investigating the death and on Thursday made a public appeal to help solve the suspected homicide.
"We know there are people out there who have information about this assault," Detective Superintendent Patrick Sharkey said.
"We need those people to come forward."
Guy Haymes' family want to know why the well-liked man was killed. (Supplied Nsw Police/AAP PHOTOS)
Mr Haymes was well-known in surfing communities spanning from the northern beaches to Wollongong, south of Sydney.
His brother said the family had been left in shock and was seeking answers about what happened to the fun-loving, sociable and well-liked man.
"Not knowing what happened that day and not having the answers is the hardest part," Mark Haymes said.
"Our whole family is shocked and in disbelief that he had his life cut short – and in such a brutal way.
"If anyone out there has any information, please come forward as our whole family needs closure."
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