So far, the investigation into Thompson’s killing has centred on a few clues that police are using to identify the suspect.

Police revealed the suspect was photographed at a nearby Starbucks just minutes before the shooting.

While he is masked in the image, police sources told CBS, the BBC’s US partner, that the mask is pulled down far enough so that his eyes and part of his nose can be seen.

With that, investigators are using facial recognition software to try to find a match.

Additionally, police are testing three bullet casings and three live rounds found at the scene for DNA.

The words “deny,” “defend” and “depose” were discovered on the casings, police sources told ABC News.

A cell phone was discovered in an alley along the suspect’s escape route. Police say they are “working through” the phone.

Investigators also said they would search Thompson’s room at the nearby Marriott, which is down the street from where the incident took place.