A 3D printer and suspected "homemade" gun components seized during police raids in Manchester are being examined.
Officers initially thought they could be a "plastic magazine and trigger" which would make a "viable" gun.
But a man who was arrested in connection with the raid said the parts were sections of the 3D printer.
Greater Manchester Police (GMP) has now said it "cannot categorically say" whether the objects are the component parts for a gun.
The arrested man, who has since been bailed, said: "It's nothing to do with a gun whatsoever.
"I have no idea why they think it is part of a gun. It's designed by the company that makes the printer to go in the printer to make it better."
The component suspected as being a magazine for a gun was in fact a "spool holder" for the 3D printer, he added.
3D printing technology works by building up layer upon layer of material - typically plastic - to create complex solid objects.
The equipment was seized during a series of raids targeting organised crime.
A force spokesman earlier said if the tests showed the parts could make a functioning weapon it would be the "first ever seizure of this kind in the UK".
But experts have cast doubt on whether the printer was sophisticated enough to print gun components.
Brian Derby, professor of material science at University of Manchester, said the seized printer appeared to be a hobbyist's machine.
He said: "It would make something that would look like a gun but it would not work as a gun."
Asst Ch Con Steve Heywood said: "We need to be absolutely clear that at that this stage, we cannot categorically say we have recovered the component parts for a 3D gun.
"What we have seized are items that need further forensic testing by national ballistics experts to establish whether they can be used in the construction of a genuine, viable firearm."
He added: "Clearly the fact we have seized a 3D printer and have intelligence about the possible production of a weapon using this technology is of concern. It is prudent we establish exactly what these parts can be used for and whether they pose any threat."
The BBC's home affairs correspondent Dominic Casciani said the manufacture of guns through 3D printing was "almost inevitable" because of the relatively few firearms in circulation.
"The worst-case-scenario would be a cheap and 100% reliable device that could be made overnight and then destroyed after just one use, disposing of crucial evidence to pin to a suspect," he added.
Desktop 3D printers can be bought on the High Street for less than £1,000, but prices more complex models can cost £10,000.
The world's first gun made with 3D printer technology was successfully fired in the US in May.
The group that created the firearm, Defense Distributed, said it planned to make the blueprints available online.
Defense Distributed is headed by Cody Wilson, a 25-year-old law student at the University of Texas, who defended making the design available by saying: "I'm seeing a world where technology says you can pretty much be able to have whatever you want.
"It's not up to the political players anymore."
At the time, Europe's law enforcement agency Europol said it feared criminals would follow suit as the technology became cheaper and more user friendly.