In the wake of Wednesday’s deadly shooting at an Immigration and Customs Enforcement (ICE) field office in Dallas, Texas, authorities said they had recovered shell casings inscribed with the words “ANTI-ICE”—marking the third high-profile attack within the past year in which ammunition was found carrying a written message.
Shell casings with the words “deny,” “defend” and “depose” were reportedly found at the scene after UnitedHealthcare CEO Brian Thompson was killed in December 2024, wording similar to a phrase used to describe procedures deployed by insurance companies to avoid paying claims.
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About ten months later, after the conservative commentator Charlie Kirk was assassinated at a university event in Orem, Utah, earlier this month, authorities said the suspect, Tyler Robinson, had etched references to obscure internet memes onto bullet casings that were found with the gun recovered at the scene.
In each of the three cases, investigators and the public have attempted to glean motives from the messages left behind. The perpetrators of ideologically motivated attacks have been known to tie their crimes to messages in the past, but the use of munitions themselves to convey such words appears to have been far rarer.
Read more: Two ICE Detainees Killed in Shooting at Dallas Facility, Suspect Also Dead
Here’s what you should know about that history—and why these inscribed shell casings might be turning up now.
Engraving shell casings goes back “hundreds of years”
Gun owners have marked their casings in a variety of ways going back hundreds of years, says Dr. Richard K. Pumerantz, an expert witness in ammunition, firearms and shooting scene reconstruction with 20 years of ammunition industry experience.
Sharpies are most commonly used to mark brass casings, Pumerantz tells TIME, though carbine-tipped or vibrating pens used for engraving metals are also easily accessible and don’t require any specialized background to use.
Most often, cartridge casings have been inscribed so that shooters can identify their bullets, he says. Participants in shooting sports, for instance, mark casings to know how many times they’ve reloaded their gun. Hunters frequently inscribe inspirational messages onto their ammunition. In World War II, the practice of inscribing munitions extended beyond bullets; bombs that were dropped from planes sometimes carried inscriptions, as did planes themselves.
But “the fact that it’s gotten notoriety now in murders,” Pumerantz says, is new.
“In the past, I think it had always been with an intention of self recovery. They weren’t really for other people to see, really for them to just simply identify those as their shell casings,” he says.
Why are these inscriptions now being used in high-profile shootings?
Like inscribing shell casings, communicating messages in connection with high-profile acts of violence has a long history. But those messages have more commonly come in the form of manifestos or notes.
Theodore Kaczynski, the domestic terrorist known as the Unabomber who carried out a string of bombings over the course of nearly two decades starting in the late 1970s, left behind a lengthy manifesto railing against “industrial society.”
Read more: Revisit TIME’s Unabomber Cover Story More Than 20 Years Later
In another prominent case, Anders Breivik sent out a manifesto over 1,000 pages that detailed a far-right ideology and copied passages from Kaczynski’s manifesto before he killed 77 people in an attack in Norway in 2011.
Eight years later, Brenton Tarrant killed 51 people in two separate shootings at mosques in Christchurch, New Zealand, after hereleased a more than 80-page manifesto filled with anti-Muslim, extremist language. The manifesto is now illegal to possess in New Zealand.
Engraving smaller messages into munitions isn’t entirely without precedent, though it hasn’t been documented with anywhere near the same frequency. In addition to his manifesto, Kaczynski also inscribed the letters “FC” into parts of his bombs. He later explained the letters stood for “Freedom Club.”
Pumerantz suggests that the inscription of the bullet casings in the recent cases “seems to be a way of leaving a memory, leaving a marker behind as a means of sending the message, knowing that it’s going to be recovered by law enforcement.”
The suspected shooters, he speculates, may be seeing the small space on cartridge casings as the only platform to express their anger or frustration—a platform “they know will deliver the aggression.”
He worries that the virality of the messages left behind on casings, as they have been publicized during investigations, increases the likelihood that this practice will be adopted by others.
“It’s a way of almost trademarking what they’re doing,” Pumerantz says. “And I think that you’ll see a lot of copycats. I think we’re going to see a proliferation of marked casings in these types of situations.”
Joseph K. Young, a political violence expert at the University of Kentucky, tells TIME that the engraved casings might be viewed as a “mini manifesto.” But he says they present challenges for law enforcement trying to find and convict perpetrators in ongoing man-hunts. In the case of Robinson, the suspect in the Kirk shooting, his messaging was “more gamer than it was political,” says Young.
In the past well-known cases of targeted violence where perpetrators left behind high volumes of political messages, including in the form of lengthy manifestos, the motives for the crimes were much clearer. There were thousands of words to draw from. But Young says the smaller inscriptions on bullets could be harder to make sense of.
“Sometimes those messages aren’t completely coherent and it’s not totally clear what someone’s trying to say. And that’s challenging, both for investigators and scholars and observers … At some level, that’s troubling, because then it’s harder for us to understand where these messages are being sent and then where people are getting radicalized.”
Speaking about the recent shootings, Thomas Zeitzoff, a professor of criminology at American University, says the motives of what he characterized as radicalized “lone actors” are less clear based on the scant messaging they leave behind.
“You get this weird kind of salad bar extremism,” Zeitzoff tells TIME, in part due to the vast access to online forums expressing different ideologies. “I think that’s like, especially with lone actors. The motive is not always going to be clear.”