Greater Manchester Police have told ITV Central they do not believe the weapon used in the murder of PCs Fiona Bone and Nicola Hughes was smuggled into the UK by Steven Greenoe.
Greenoe, a former US Marine who lived in Shrewsbury, was jailed for ten years in January for a major gun-smuggling operation from America into the UK on commercial transatlantic flights.
The GMP told ITV Central: "There is no evidence to suggest the guns came from him. It is not a line of inquiry."
Officers nationwide have offered cover to colleagues in Greater Manchester Police so they can attend the funerals of the two killed PCs.
Manchester's police chief said he expected "developments" in the next 24 hours over possible charges relating to the deaths of two officers.
Over 50,000 tributes have been posted to Greater Manchester Police's online book of condolence to the two killed officers and Facebook page.