A device that prompted a bomb scare at Wollongong Botanic Garden earlier this week was discovered in a building inaccessible to the public.
The device - an unsophisticated assembly of materials - is being examined by police for clues to its provenance.
Authorities are closely guarding the list of ingredients involved in making the "suspicious item", partly for fear of copycats.
It was found on Wednesday in a former residence used to store materials for the garden.
According to Wollongong City Council, a staff member at the Botanic Garden made the discovery after first noticing signs of forced entry to the residence.
Wollongong's Inspector Tim Beattie said the device, and the intention behind it, remained the subject of an investigation.
"It wasn't a sophisticated device but, taken together, it would be capable of causing an explosion," he said.
"We can't speculate as to what it could be, it could be a number of things but at the moment we are following several lines of inquiry.
"If anyone has any information about who opened that room, or was seen to go into that room, we'd be very keen to hear from those people."
Contact Wollongong Police Station: 4226 7899, or Crime Stoppers: 1800 333 000.