The morning of December 4, 2024, changed a lot of things. Not just for the family of Brian Thompson or the corporate halls of UnitedHealthcare, but for the way we talk about modern firearms. When the news broke that the CEO had been gunned down in midtown Manhattan, everyone had the same question. It wasn't just "who" or "why," but "how."
Specifically, what gun did United Healthcare shooter use?
The grainy surveillance footage showed a hooded figure. He looked methodical. Calm, even. But the gun—that’s what caught the eye of every ballistics expert and hobbyist watching the feed. It didn't sound right. It didn't cycle right. Honestly, it looked like something out of a low-budget spy movie.
As it turns out, the reality was much more "DIY" than anyone expected.
The Mystery of the Ghost Gun
When Luigi Mangione was finally cornered at a McDonald's in Altoona, Pennsylvania, his backpack wasn't just full of fake IDs and a manifesto. It held the smoking gun. Literally.
Police recovered a 3D-printed ghost gun.
Now, "ghost gun" is a term that gets thrown around a lot in the news, but basically, it just means a firearm without a serial number. It’s untraceable because it wasn't born in a factory like a Smith & Wesson or a Glock. It was born in a living room or a garage.
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Why the Gun Malfunctioned on Video
If you’ve seen the footage, you saw the shooter struggle. He had to manually rack the slide after his first few shots. You've probably wondered: if he planned this so carefully, why was the gun such a mess?
The weapon was a 9mm pistol, but it was a hybrid. It used a 3D-printed lower receiver (the plastic part you hold) paired with a metal slide and a threaded barrel. Specifically, experts pointed to a design known as the Chairmanwon V1 or a variation of the FMDA 19.2. These are files you can find on the darker corners of the internet.
The issue? Homemade suppressors.
Mangione was using a 3D-printed silencer (suppressor). These things are notoriously finicky. They create backpressure. If the dimensions aren't perfect, the gas doesn't cycle the slide back far enough to load the next round. That’s why he had to keep clearing it manually. It's the trade-off for staying quiet.
Technical Specs: What Was Actually in the Bag?
The Pennsylvania criminal complaint gave us the most "under the hood" look at the hardware. It wasn't just a plastic toy; it was a lethal, albeit janky, piece of engineering.
- Caliber: 9mm (Full Metal Jacket and Hollow Point rounds were both found).
- Magazine: A standard Glock magazine (some reports mention Magpul as well).
- Frame: A black 3D-printed plastic handle/receiver.
- Upper: A metal slide with a metal threaded barrel to accommodate the "can" (the silencer).
The 3D-printed suppressor was the real outlier here. Usually, people who build ghost guns still buy metal suppressors because plastic ones tend to... well, melt or explode after a few rounds. This one held together long enough to do the job.
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Why This Specific Weapon Matters
For years, people treated 3D-printed guns like a curiosity. A "what if" scenario. This event made it a "right now" reality.
Think about it. Mangione was a UPenn grad with a background in computer science. He didn't need a shady back-alley deal. He just needed a printer and some CAD files. Because the lower receiver (the part the ATF actually considers "the gun") was printed, there was no background check. No paper trail. Nothing.
Initially, there was a lot of chatter about the B&T Station SIX or a Welrod. Those are professional-grade, bolt-action "assassination" pistols. They look similar to what was used because of the long, integrated suppressor look. But those are hard to get. They require federal stamps and deep background checks. Building a "plastic Glock" was the path of least resistance for someone who wanted to disappear.
The "Delay, Deny, Depose" Connection
The gun is only half the story. The ammo told the rest.
The shell casings found on the sidewalk weren't just brass. They were "message boards." Written in Sharpie were the words "Delay," "Deny," and "Depose." These are the three pillars of what critics call the "Insurance Company Playbook."
It’s rare to see a weapon so tightly integrated into a motive. The gun was homemade to bypass the system. The messages were written to attack the system. It’s a chilling combination that has law enforcement rethinking how they track "lone wolf" actors who have the technical skill to manufacture their own lethality.
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What This Means for Gun Laws in 2026
Since this happened, the legal landscape has been a total whirlwind. New York and other states had already started cracking down on "unfinished receivers," but the Mangione case pushed things into overdrive.
We’re seeing more focus on digital file sharing. Is a CAD file for a gun frame protected speech under the First Amendment? Or is it a public safety threat? The Supreme Court has been chewing on cases like Garland v. VanDerStok, and the UnitedHealthcare shooting is basically Exhibit A for the prosecution.
Actionable Insights for the Future
If you’re following this case or concerned about the tech behind it, here is what you need to keep an eye on:
- Serialization of Parts: Watch for new laws requiring serial numbers on slides and barrels, not just the frame.
- 3D Printer Regulations: Some jurisdictions are proposing "background checks" for high-end 3D printers or software locks on certain file types.
- Ghost Gun Detection: Tech is being developed for "ballistic signatures" of 3D-printed barrels, though it's still in the early stages.
The weapon used in the UnitedHealthcare shooting wasn't the most powerful gun in the world. It wasn't even the most reliable. But it was untraceable, quiet, and easily made by someone with a laptop. That’s why it changed the conversation forever.
To stay informed on the trial and the evolving ballistics evidence, keep a close watch on the federal court filings in the Southern District of New York. The technical details of that 3D-printed suppressor are likely to be a major focal point as the defense tries to suppress the evidence gathered from the backpack in Pennsylvania.