What to know about 'ghost guns,' the weapon allegedly tied to the CEO shooting

The man arrested Monday in connection with the fatal shooting of UnitedHealthcare CEO Brian Thompson is alleged to have had a type of homemade weapon known as a "ghost gun."

Luigi Mangione, 26, whom police named as a “strong person of interest,” had a "ghost gun that had the capability of firing 9 mm round and a suppressor” when he was arrested on weapons charges in Altoona, Pennsylvania, New York Police Department Chief of Detectives Joseph Kenny told reporters.

A senior law enforcement official told NBC News the weapon found in Mangione's possession appears to be similar to the weapon used in the Manhattan murder. Kenny said the weapon "may have been made on a 3D printer."

What are ghost guns?

"Ghost guns" are firearms that can be assembled at home from parts that are bought online. Those parts can usually be obtained without background checks and do not have serial numbers.

How long have ghost guns been around?

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The do-it-yourself kits have been around since the 1990s, but they have exploded in popularity in recent years — especially among criminals.

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives said that from January 2016 to December 2021, it received about 45,000 reports of suspected privately made firearms recovered by law enforcement agencies in criminal investigations — including 692 homicides or attempted homicides. 

The number of ghost guns recovered rose steadily each of those years, from 1,758 in 2016 to 19,344 in 2021, according to the Justice Department.

Technology has also added to the steep increase — online videos about how to assemble the guns have millions of views, while some sellers offer 3D printing files for customers to print and assemble the weapons themselves, without serial numbers.

The Justice Department said in a 2022 fact sheet that firearms without serial numbers are incredibly difficult to trace — the ATF reported it was able to trace only 0.98% of the suspected ghost guns submitted by law enforcement to individual purchasers.

What is the government doing about the issue?

In 2022, President Joe Biden announced restrictions on the sale of ghost guns with the finalization of a rule requiring makers of gun kits to include serial numbers on firearms and sellers to follow the same standard as with other guns, including requiring background checks for purchases.

“These guns are the weapons of choice for many criminals,” Biden said, and “we are going to do everything we can to deprive them of that choice.”

Gun rights groups and manufacturers have challenged the ATF rule in court, with a federal judge in Texas and an appeals court ruling against the Biden administration.

The U.S. Supreme Court heard oral arguments on the Biden plan in October and will issue a final ruling in the coming months. The high court has ruled twice that the rule can remain in place in the meantime.

Gun safety advocates, meanwhile, have been urging Congress to close loopholes and turn the rule into a law. Over a dozen states have also passed laws regulating ghost guns, according to Everytown for Gun Safety, a gun violence prevention organization.

The group and others have also been urging Congress to take action on 3D-printed guns, which the Trump administration loosened regulations on in 2020. No federal law bars them, but the ATF says that it is illegal to make them for sale without licenses and that they must be detectable by metal detectors and X-ray machines. A number of states also have individual laws regulating or banning the weapons, according to Everytown.