The man held in the December 4 killing of UnitedHealthcare CEO Brian Thompson used a “ghost gun” – a type of homemade firearm made with a 3D printer or from parts sold online.

Luigi Mangione, 26, was in possession of a “ghost gun capable of firing 9mm cartridges and a silencer” when he was arrested, NYPD Chief Detective Joseph Kenny told reporters on Dec. 9.

What are Ghost Guns?

Ghost guns are unregistered and untraceable homemade weapons.

They typically come in do-it-yourself (DIY) kits and are shipped in pieces, allowing buyers to complete the final assembly themselves.

They can also be made with a 3D printer. Once assembled, ghost guns are fully functional deadly weapons.

There are kits for a dizzying variety of firearms, including Glock 9mm pistols, AR-15 and AK-47 assault rifles, and shotguns.

What makes ghost guns so tempting?

Ghost guns are easy and relatively inexpensive to assemble.

“You can buy a box of firearm parts and put those firearms together, and I’ve seen videos on YouTube where you can see people doing that in record time – 20, 30 minutes,” said Mr. Marvin Richardson, the current deputy Director of the US Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) in a CBS News report in 2022.

The DIY kits cost less than US$200 (S$268) when purchased in the US, although officials put the average price at about US$500.

Ghost guns have been around since the 1990s, mostly as under-the-radar oddities.

They became mainstream in recent years with a flood of online videos that included instructions on how to assemble, customize and modify them.

Recently, sellers are also providing blueprints and schematics that allow 3D printer owners to easily make the parts themselves.

“Today, people can sit at home in their living room, log on to their computer, access some software, send a signal to their printer and print out a machine gun that can kill people. That’s a problem,” said John Miller, CNN’s chief law enforcement and intelligence analyst.