Charlie Kirk shooting criminal hunt included a rare forensic tech tip

As the search unfolded for conservative political activist Charlie Kirk’s assassin, with the suspect identified on Friday as Tyler Robinson, law enforcement parsed every possible lead. One piece of evidence they homed in on: a forearm print taken from the sniper’s position.

Before Robinson’s apprehension Friday morning as a result of very human methods — it has been reported that Robinson offered what may have been a form of confession to family members, who then shared the information, leading to his surrender, though the situation is fluid and more details on the investigation were offered over the weekend — FBI agent Robert Bohls said investigators had collected a “footwear impression, a palm print and forearm imprints” from the crime scene for analysis.

Forearm imprints are not a commonly collected piece of evidence, according to experts CNBC spoke with.

“It’s very unusual,” said Patrick McClain, a Texas-based criminal defense attorney and retired Marine Corps military judge. McClain explained that typically, when a forearm print is mentioned, authorities have collected DNA or other skin residue from the surface against which the forearm was pressed.

“It’s merely a mold from an imprint left from remaining in a prone shooting position with forearms on the deck for a period of time,” said Jeff Wenninger, founder and CEO of Law Enforcement Consultants, who has worked with the LAPD’s elite Metropolitan Division and with the Secret Service in protecting dignitaries. “It would be similar to a shoe or boot print that they lift with a mold,” he added.

Wenninger says that a forearm print can be used to corroborate identification purposes, such as unique characteristics like scarring or the imprint of known clothing worn.

“Like fingerprints, a forearm print can be unique enough for identification if it’s of sufficient quality,” he said.

It could also have a forensic value if biological material like sweat, body oils, or touch DNA can be recovered, and along with other evidence, it can corroborate or contradict witness statements or video footage.

New technology is giving the forearm a wider window into a possible suspect. Physical impressions have been utilized in forensic investigations for years, Wenninger said, but in recent years, the methodologies for identifying and comparing specific meaningful markings have evolved, and the scanning technology for analyzing imprints has improved so much that “it seems new.” 

3D scanning has revolutionized this science, turning the forearm print into a reservoir of previously untapped information. An imprint alone cannot determine factors such as ethnicity and gender, and investigators would still be reliant on whether DNA or other biological evidence has been obtained from the imprint.

“It’s a newer exploration in forensics, including other skin prints. But it’s not like a finger/palm print that is 100% unique,” said Toby Braun, CEO and Founder of American Special Investigative Group, which specializes in executive protection, threat-intelligence monitoring, and complex investigations.

According to Braun, a forearm print won’t ID a person from a database like a fingerprint would. “A forearm print is not considered a primary form of forensic evidence in the same way that a fingerprint is,” he said.

A forearm print isn’t a primary form of evidence because there can be ambiguity, according to Braun. For example, while the friction ridges on fingers and palms are unique to each individual, the skin on the forearm does not possess the same detailed, permanent, and individualized ridge patterns.

The difficulty with forearm residue is that even in the most high-profile cases, any DNA would take a while to get results from, and that if the person is not in a known database, it won’t be beneficial until there is an arrest. “There are not going to have been too many people on the roof of the building,” McClain said. “But it is not like a fingerprint; there is no unique structure to everyone’s forearm.”

According to McClain, there have been cases tried with forearm prints if there is something unique, such as a tattoo or scarring pattern, “but I have never done one of those cases; they are definitely unusual,” he said.

As in any manhunt, in the hours after the shooting, the focus was on finding the shooter and making an arrest. “Additional evidence for the strongest possible case will be developed subsequently as the investigation is still ongoing,” Braun said, adding that authorities just need probable cause for an arrest, and evidence beyond a reasonable doubt is for a trial. “But that is developed as the case progresses,” he added.

Dan Gerl, founder and managing attorney at Next Law, says that for a forearm’s “pattern” to be lifted or photographed as evidence, the subject would have had to apply sufficient pressure upon a receptive surface area and that the prints are most useful as supporting evidence rather than primary, such as to support a request for a search warrant seeking additional evidence.

“Under certain circumstances, forearm prints can also be admissible in court. Like all scientific evidence, forearm prints would have to be admitted by a qualified expert’s testimony, and pass the court’s tests for reliability,” Gerl said. This type of forensic evidence would likely encounter more procedural hurdles to clear before being admitted at trial, he added.

Robinson was arrested on suspicion of aggravated murder, felony discharge of a firearm, and obstruction of justice by police. Prosecutors will ultimately decide the charges he faces before the court, which are expected to be filed on Tuesday.

In the end, the arrest of Tyler Robinson came down to human rather than forensic connections, and some criminal experts say a defining feature of recent political violence is a killer’s underlying desire to be caught rather than meticulously plan and evade capture.

Bryanna Fox, a former FBI special agent and professor of criminology at the University of South Florida, says advances in crime technology have been notable over the past two decade, and some criminals may not be aware of the level of forensics available to law enforcement. “He may have thought, ‘Oh, I can leave my forearm prints and it won’t amount to anything,” Fox said.

But she thinks that another mindset may have been at work. Comparing the Robinson case to the case of Luigi Mangione, who assassinated a United Healthcare executive last year, Fox thinks ideologically driven criminals may care more about sending a message than about escaping consequences for their crimes.

That means they may not be thinking about the trail of evidence they leave behind as much as some other criminals, whether prints, covering their face, or how they dispose of a weapon. “The attention helps give more oxygen to what an ideologue wants to say,” Fox said. “In a way they are sort of stipulating to the fact that they will get caught and are OK with leaving some evidence. They don’t want to get caught right away, but their main mission is to achieve the goal, which is to kill their target,” she added.