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…