CHICAGO (CBS) – Shots picked up on the crime fighting technology called ShotSpotter is what brought Officers Conrad Gary and Eduardo Marmolejo to the train tracks nears 101st Street and Cottage Grove Avenue within seconds of a shot.

PO Conrad Gary and PO Eduardo Marmolejo (Twitter)

RELATED: Two Police Officers Hit And Killed By Train On The South Side

They were the first to respond.

“We’re close. We’ll ride over,” they can be heard saying over police radio.

They ran up the embankment, and sources tell CBS 2’s Dorothy Tucker the officers climbed through holes in the fence to chase a gunman.

From the body cam footage, police say the officers were traveling south, and a train was coming toward them on another track.

Police believe they may have been distracted by the oncoming train and didn’t hear the South Shore train that was coming behind them before it made impact.

Authorities say the train operator was traveling about 65 miles per hour and slammed on the brakes but couldn’t stop.

Sources tell CBS 2 the operator “knew he had hit someone.” He told his dispatcher, “It looks like he may have been wearing a uniform” and that he “definitely hit somebody.”

The source goes on to say, “The conductor then got off the train, walked to the back and encountered a gruesome scene.”

“It was just crazy. I mean it happened so quick,” witness Greg Brewer said.

About a minute after the impact a dispatcher announced the man the officers may have been chasing had been caught. He called the officers to tell them.

“You all copy? One in custody, one weapon recovered,” the dispatcher said over the radio.

They never responded. But after a fellow officer asked the dispatcher called again and again.

Finally, the officer figured they were busy, obviously unaware of the tragic outcome.

“Disregard. I see flashing lights a half mile down the tracks. Hopefully the train has stopped,” an officer can be heard saying.

Railroad employees, train operators and staff have been offered counseling.

Sources say the suspect was picked up on the street near the tracks. He reportedly told police he found the gun and fired it into the air to see if it worked. Police did find shell casings on the tracks.

Dorothy Tucker