Is there proof that people who are not allowed to have guns are printing guns?

In February 2019, a Texas man was sentenced to 8 years in prison after officers caught him with a partially 3-D printed AR-15 rifle and a list of lawmakers’ addresses in his backpack, despite being prohibited from owning a firearm due to a violent altercation with a live-in girlfriend. And, while we don’t know how many 3D-printed guns exist, we know unserialized guns comprise a significant proportion of crime guns recovered by law enforcement.