The only part that didn’t come from a 3D printer is the string stretched across the crossbow’s arms, and whatever’s used for ammo—whether it’s a chopstick or a balsa glider.

In states like New Jersey, assembling a 3D-printed gun is illegal without obtaining a federal license, and the sale of other forms of untraceable guns is also criminalized, according to The Trace.

When the digital blueprints for JStark’s FGC-9, a semiautomatic pistol calibre carbine, were released online in March 2020, it marked a watershed moment in 3D-printed and do-it-yourself firearms.

Police said Luigi Mangione, the man charged in the killing of UnitedHealthcare CEO Brian Thompson, appears to have had a ghost gun, a weapon that can be made using a 3D printer.

Part of the gun that the police believe was used to kill the C.E.O. of UnitedHealthcare was made by a 3D printer using a popular design found online. By Thomas Gibbons-Neff and Aric Toler At first ...