Homemade 'ghost guns' face federal scrutiny as DOJ proposes new regulations on the firearms that are impossible for police to track The Justice Department said in its 115-page proposal that, from 2016 to 2020, the ATF had recovered 23,906 firearms that did not display serial numbers The department said ghost guns were linked to at least 325 murders or attempted murders in that period Some manufacturers have exploited loopholes to sell the hardest-to-make gun components, the upper and lower receivers, without engraved serial numbers Kits for the firearms are also being sold at gun shows without requiring background checks for buyers The document noted that the lack of serial numbers makes it difficult for law enforcement to determine 'where, by whom, or when they were manufactured'