The incident unfolded on Tuesday evening when Joshua Cummings, 37, allegedly walked up to transit security officer Scott Van Lanken and opened fire.
Van Lanken, 56, died from his injuries while en route to the hospital.
Cummings fled the scene but was located a short time later. Sources said that the suspect was found in possession of radical jihadist material at the time of his arrest.
It was unclear if the ambush was due to the impression that Van Lanken was a police officer given his uniform looked similar to local law enforcement. Police have been told to remain vigilant nonetheless.