The murder of a top health insurance executive is bringing fresh attention to Connecticut’s ban on “ghost guns” – homemade firearms with no serial numbers and no way for police to trace them.

Connecticut was one of the first states to ban unserialized guns five years ago. But is it working?

Police arrested Luigi Mangione, the suspect in the murder of UnitedHealthcare CEO Brian Thompson, eating breakfast at a McDonald’s in Altoona, Pennsylvania. Inside his backpack, they found a 3D-printed pistol and silencer, according to a criminal complaint.

“The gun looks very similar with the similar suppressor” to the gun used in Thompson’s ambush, New York Police Commissioner Jessica Tisch told ABC’s “Good Morning America.”

Mangione is being held without bail in Pennsylvania on charges of possession of an unlicensed firearm, forgery and providing false identification to police. He contested his extradition back to New York at a court hearing, where he is charged with murder.

Here in Connecticut, Stamford police say “ghost guns” are some of the most dangerous weapons on the street. Since anybody can make one with a 3D printer and parts ordered online, they are particularly attractive to criminals.

“We’ll find them in any instances between – anywhere from homicides to shootings, assaults,” said Major Crimes Sgt. Sean Boeger. “People that are ineligible to possess firearms, either because of criminal record or a mental health history or any of the issues that would raise the red flag system.”

A News 12 Kane in Your Corner investigation showed how easy it is to order and assemble a homemade gun – and how difficult they are to regulate.

Connecticut banned firearms without serial numbers in 2019. But a loophole made the ban virtually unenforceable, so lawmakers tweaked it last year as part of a sweeping gun control package.

Violence prevention groups believe the law is working.

“In 2019, the state confiscated probably, roughly 53 to 60 ‘ghost guns,’” said Earl Bloodworth, president of Connecticut Against Gun Violence. “After that, it was a lot more.”

Connecticut is also going after online suppliers. Attorney General William Tong sued four retailers last year for allegedly selling kits to assemble illegal guns, including AR-15 assault-style rifles.

“This is an 80% lower receiver for an AR-15,” Tong said in March 2023. “It is highly illegal to sell these parts here in Connecticut, and if you do that, we are going to come after you.”

The state has settled with two of the companies. The cases against two other defendants remain pending – including Indie Guns, whose owner admitted to News 12 that he never checked whether his products were legal.

“There’s so many laws; they change by the week, alright?” Indie Guns owner Lawrence DeStefano said in March 2023. “I don’t have time to keep up with these laws.”

Private citizens are allowed to build guns for personal use under the Gun Control Act of 1968, but more than a dozen states now require them to have serial numbers.

Gun rights groups have argued that homemade firearms are simply a hobby for gun enthusiasts – and not a major crime problem.

“As far as a criminal is concerned, it is far easier for them to steal a firearm and to obliterate the serial number than it is for them to manufacture a functioning firearm at home,” Aidan Johnston, with Gun Owners of America, told Kane In Your Corner.

Stamford police have seized three “ghost guns” this year and six of them last year.

“How much of a problem is that?” said Sgt. Boeger. “I don’t know. How many homicides are acceptable before some kind of regulation is in place?”

Nationally, the problem is growing much faster. “Ghost gun” reports jumped from 1,758 in 2016 to 19,344 in 2021 – a 1,000% increase in five years – according to the federal Bureau of Alcohol Tobacco and Firearms.

ATF now requires weapons assembled from a kit to have serial numbers, just like traditional firearms.

"If you commit a crime [with a] ghost gun, not only are state and local prosecutors going to come after you, but expect federal charges and federal prosecution as well," President Joe Biden said in 2022.

But kit manufacturers are challenging the rule in court, and the incoming Trump administration may roll it back. The U.S. Supreme Court heard the case in October.

Efforts to pass a “ghost gun” law in Congress have stalled and are unlikely to move forward when Republicans take over in January.