A major NSW Police operation kicked into gear on Sunday, after investigators initially believed the suitcase, found by two members of the public at Oallen, about 60km southeast of Goulburn, contained a women's body.
But by 10am on Monday forensic investigations revealed the contents of the suitcase were not human after all.
"We are still undertaking more forensic work to identify what they are, but we can identify that they are not human," Superintendent Linda Bradbury told reporters in Goulburn.
"They were mistaken for a human originally, so they are very realistic in the terms of looking like human remains ... but we have confirmed they are not."
Police were unable to confirm if they were animal remains or something else.
When pressed about how the force could make such an error, Supt Bradbury said police followed the correct process of investigating a major crime.
"We followed our processes to the tee, to a high level and I think there's no regrets at all," she said.
"I couldn't be more proud of my team than I am."
The suitcase was found by two men who had pulled onto the side of the road by chance.
"They were on a weekend drive as a lot of people do over the weekend and stopped for a break. (It was) quite a shocking discovery for them, absolutely," Supt Bradbury told Nine's Today.
It was unclear how long the suitcase had been there and officers were initially trawling through unsolved missing person cases.
It was found in remote bushland with few properties nearby and hardly any traffic.
A crime scene was set up and Homicide Squad detectives travelled to the area in the Southern Tablelands region of NSW.
Forensics officers faced challenging conditions on Sunday night as they worked to gather any evidence left behind before it was washed away by rain.
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