As two Chicago police officers tried to locate the source of gunshots on the city’s South Side Monday night, they scrambled up an embankment and onto a set of southbound train tracks, walking south and keeping an eye on a northbound train as they searched for the potential shooter. Police officials said Officers Eduardo Marmolejo, 36, and Conrad Gary, 31, likely never heard the southbound train coming up behind them. According to The Chicago Tribune, one officer’s body camera footage offered investigators a glimpse into what took place as both men were killed. “They had no idea the train was behind them,” Anthony Guglielmi, a Chicago police spokesman, told the Tribune. “They hear the noise (of the northbound Metra train), we suspect. That masks the noise of the other train that is right behind them.” The oncoming South Shore train struck the officers on a viaduct over 103rd Street, the Tribune reported. They were killed instantly. >> Read more trending news The newspaper reported that it was not yet known how fast the South Shore train was going, but Michael Noland, CEO and president of the Northern Indiana Commuter Transportation District, said South Shore trains typically go around 65 mph on that stretch of track. The company, which operates South Shore trains on the city’s Metra tracks, is downloading the train’s event recorder to turn over to police investigators. Police Superintendent Eddie Johnson said Monday night that Marmolejo and Gary, both relatively new officers on the force, responded shortly after 6 p.m. that evening to 103rd Street and Dauphin Avenue when the city’s ShotSpotter system picked up the sound of gunshots. “While doing the most dangerous thing a police officer can do -- and that is to chase an individual with a gun -- these brave young men were consumed with identifying a potential threat to their community and put the safety of others above their own,” Johnson said. Guglielmi told the Tribune that the body camera footage shows the officers get out of their patrol car after spotting someone who could have been the shooter. They cross the viaduct and head south in the direction they apparently believe the suspect is moving. “They were deciphering the offender’s direction of flight,” Guglielmi told the newspaper. A gun and shell casings were found near where the officers died, the police spokesman said. A person of interest was being questioned in the case Tuesday, the Tribune said. Johnson said Monday night that Marmolejo had been on the force for more than two years. Gary was on the force for 18 months. According to the Officer Down Memorial Page, Marmolejo is survived by his wife and three children. Gary, a U.S. Air Force veteran, is survived by his wife and an infant daughter. Chicago Mayor Rahm Emanuel was subdued as he spoke of the effect the officers’ deaths on the department, which has lost two other officers in the line of duty this year. “I’m not usually one for a loss of words, but I think you can understand the idea in trying to express the immense sense of devastation to the Chicago Police Department,” Emanuel said. He praised Marmolejo and Gary for working to keep their community safe, at the expense of their own lives. “There they were, responding to ShotSpotter, doing their job trying to protect the rest of us,” the mayor said. “We’ve lost two young men, both fathers with young families. This holiday will never be the same for those two families, and while our hearts are with them, we’ve lost people who answered the call to make Chicago a better place.” Emanuel said he spoke to one of the families alongside the superintendent. “There are no words that can express the grief, the sense of loss -- it just knocks you back on your heels,” Emanuel said. “As we go about our time with our families, let us remind ourselves that there are others who cannot.” Marmolejo and Gary are the third and fourth Chicago officers slain in the line of duty this year. Officer Samuel Jimenez, 28, was one of four people who died, including the gunman, in a Nov. 19 mass shooting at the city’s Mercy Hospital & Medical Center. The other victims in that shooting were Dr. Tamara O’Neal, 38, and 24-year-old pharmacist Dayna Less. All three were killed by O’Neal’s former fiancé, 32-year-old Juan Lopez, who then killed himself. Cmdr. Paul Bauer, 53, was killed the afternoon of Feb. 13 when he attempted to help other officers take into custody a fleeing man sought for questioning in a previous shooting. The Tribune reported that officers had approached Shomari Legghette, a four-time felon, to question him when he ran away on foot. Bauer, who was in downtown Chicago for a meeting after a morning of training on mass shootings, heard the call over his radio and, after spotting Legghette running by, joined the chase. The 31-year police veteran got into a struggle with Legghette in a stairwell of a state building, where he was shot six times, the newspaper reported. Bauer’s weapon was in its holster and his radio and handcuffs were found next to his body. The Tribune reported that Legghette has been indicted on 56 felony counts of first-degree murder, armed violence, weapons and drug offenses. Marmolejo and Gary were assigned to the department’s Calumet District, which has lost three other officers this year. Two died of suicide and a third, Officer Vinita Williams, 47, died after collapsing at the station in July, the Tribune said.