What are 'ghost guns' like the one found with suspect in killing of a UnitedHealth CEO?

The U.S. government has argued that ghost guns are meant for crime because they are made from parts that can be bought online or even 3-D printed without the serial numbers ordinarily used to trace guns or background checks on purchasers required for other firearms.

Here are some facts about ghost guns and how they are made:

**Ghost guns have no serial numbers. Owners of such guns, by making them themselves, can bypass background checks and regulations.

**The administration of U.S. President Joe Biden has argued that ghost guns are meant for crime. In 2022, the administration issued a rule to rein in such guns. The Supreme Court in October signaled it is willing to let the regulation, which has been challenged, stand.

**Supporters of ghost guns say they are meant for hobbyists. They also argue that people have the right to build such weapons under the Second Amendment.

**Kits for ghost guns can be purchased online or at gun shows, as long as the frames are not fully functional. Users can easily and cheaply machine and assemble them.

**To stay within federal law, the frames or "receivers" of such guns can be sold 80% complete. The other components required to build a functioning firearm are often sold along with the frame and packaged as a kit.

Also included are drill bits and jigs that allow the purchaser to mill the frame with a simple drill press that can cost less than $100.

**The guns can be made by 3-D printing. That is the process of making a physical object from a three-dimensional digital model, including layers of plastic, metal or other materials.

**A U.S. federal law bans guns that do not contain enough metal to be detected by screening machines in public places, such as airports and courthouses, but does not require that the metal parts be non-removable. Makers of plastic 3-D printed guns have created metal inserts that are not essential for the gun to function.