Police in Dallas are asking for the public’s help to identify two suspects they said killed a 52-year-old armored car guard shot Friday morning.

David Ruback, the guard, was shot around 9:30 a.m. Friday during a robbery in the 100 block of South Carroll, according to police. No arrets have been made, but police have released still images of two suspects and their vehicle from surveillance footage.

In the stills, the suspects are seen wearing all black from head to foot and carrying rifles. The vehicle is an older model white Chevrolet Impala. No distinguishing features were visible in the images and the license plate on the vehicle, which may be a temporary paper plate, is not legible.

Police also released new details about what happened in the robbery leading to Ruback’s killing.

Investigators believe the two men attacked while Ruback and his partner, who police have not released any information about, were making a cash delivery to a business, according to police. Ruback was walking toward the door of of the business when one of the suspects approached and shot Ruback.

Police said the suspect picked up the courier bag Ruback was carrying the business’ cash in and left the scene in the white Chevrolet.

Ruback was taken to the hospital where he died. Police have not located the car the suspects used.

Anybody with information on the suspects or the vehicle should call 911.