Police were called to do a welfare check at a Burpengary East home on Thursday morning where they found two people in their 70s with serious head injuries.
The man was declared dead at the scene while the woman was rushed to hospital in a life-threatening condition.
A 26-year-old Boondall man was taken into custody after he waited at the property for police.
A house north of Brisbane has been declared a crime scene following the death of an elderly man. (Darren England/AAP PHOTOS)
Detective Inspector David Harbison said it was not a domestic violence-related incident and the 26-year-old man was not previously known to the victims.
"We believe he just attended today to do some form of gardening duties," Det Insp Harbison told reporters on Thursday.
Police are not looking for any other persons of interest.
Det Insp Harbison described it as a tragic and devastating incident.
"It is so terribly traumatic for anyone to see this, including first responders," he said.
"We hope to get to the bottom of it and learn more and try and understand how this incident occurred."
A crime scene has been established while investigations are underway.
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