Although the U.S. flag is at half-staff to mark the death of President Jimmy Carter, 8 Republican-led states will raise flags for Trump's inauguration ...

The first known criminal case involving a 3D-printed gun resulted in the arrest of a U.K. man in 2013. But since then, police worldwide have reported finding increasing numbers of these weapons.

But that has begun to change. Advancements in 3D-printing technology have yielded increasingly reliable 3D-printed firearms, many of which require no federally regulated components to function.