INDIANAPOLIS (WISH) — UnitedHealthcare CEO Brian Thompson was fatally shot Wednesday morning in New York City and the gunman remains at large. An Indianapolis-based retired FBI agent says digital evidence will be the key to finding him. 

The 50-year-old was on his way to speak at the health group’s investor conference inside a hotel. Video shows the moment he was approached by a gunman and killed. Police claim the killing was a “premeditated, preplanned targeted attack.”

“Has to be some sort of a disgruntled person, be it an employee or a policyholder, that takes somebody that clearly had a grudge with this guy, because this was a targeted attack,” retired FBI agent and CEO of Veracity IIr Doug Kouns said. 

Kouns said there are a few key signs that indicate an attack like this is targeted, especially in this case. 

For example, the gunman in Wednesday’s attack was seen lurking in the area for quite some time, Kouns said. “If somebody knows what they’re doing, they’re going to do their homework,” he said. “So, they’ve probably done some surveillance, they know they’re travel routes and patterns and life patterns.”

After looking at surveillance photos from the moment Thompson was approached, Kouns said he believes the gunman’s firearm malfunctioned and that his handling of the malfunctions indicates he had prior experience with guns. 

“There’s a variety of ways it can happen, but usually what happens is called a stove pipe, where the last round fails to eject completely, and if the next one comes up it gets pinched in the chamber,” Kouns said. 

He said it could take months to solve, but establishing a timeline will be essential. 

Digital evidence will play the largest role in setting that timeline. 

“New York, in that area specifically, I think there’s more cameras there than probably anywhere else in the world, and law enforcement should be able to put together a trail based on ‘this camera that saw him from here to here, and this business captured him from here to there and so on and so forth,’” Kouns said. “It might take a while to track down, but hopefully they’ll find some clues.”