Chicago, IL – The two Chicago police officers who were killed by a train while searching for an armed suspect on foot were struck from behind, and never saw the train barreling towards them, according to the department.

Chicago Police Officers Conrad Gary and Eduardo Marmolejo had responded to the area of Dauphin Avenue and 103rd Street just before 6:20 p.m. on Monday, after a ShotSpotter sensor detected gunfire in the area, the Chicago Tribune reported.

Earlier reports indicated that Officer Gary, 31, and Officer Marmolejo, 36, spotted a suspect running up onto the Metra tracks, and began chasing him on foot, but Chicago Police Department spokesperson Tom Ahern later said the officers had not yet located the gunman they were pursuing, WBBM reported.

Investigators were able to review the officers’ body cameras to help determine what occurred in the moments before the fatal collision, Ahern explained.

According to the department, the video showed Officers Marmolejo and Gary as they exited their patrol vehicle and walked up a hill towards the Metra tracks while discussing which direction the suspect might have gone, WLS reported.

Ahern said that the officers were facing a northbound train that was traveling in their direction on a neighboring track as they walked along the railway, according to WBBM.

They did not see the southbound train barreling towards them from behind, he explained.

The noise from the train they were watching likely drowned out the sound of the train heading towards their backs, Ahern added.

The conductor said he tried to stop the southbound train – which was traveling between 60 and 70 miles per hour – but it was too late.

The department said that Officer Gary and Officer Marmolejo were killed instantly, WLS reported.

“These brave young men were consumed with identifying a potential threat,” CPD Superintendent Eddie Johnson said during a Monday night press conference outside the agency’s headquarters, according to the Chicago Tribune.

He said the department was in “shock” over the loss of two of its own, and that the tragedy illustrated the danger law enforcement officers face every day.

“I often say the most dangerous thing a police officer can do is take a weapon off of an armed individual, and that’s what they were doing… putting the safety of others above their own,” Superintendent Johnson said, according to WLS.

Investigators recovered a weapon near the site of the impact, and were questioning a subject on Monday night, Guglielmi told the Chicago Tribune.

Police later said the suspect may have been “test firing” the weapon, and that he never fired it at the officers, WLS reported.

Northern Indiana Commuter Transportation District Spokesman Mike Noland said there were between 500 and 600 passengers on the train Number 119 on Monday night, the Chicago Sun Times reported.

No one on the train was injured in the crash, Noland said.

“You heard the train screech, like come to a screeching halt,” witness Greg Brewer recalled, according to KKTV.

Brianna Medina, who was on the train at the time of the collision, said that she and her fellow passengers knew that something was wrong, but that they initially were unaware of what caused the train to come to a stop, the Chicago Tribune reported.

“It kind of felt like rocks, and it sounded like it was hitting rocks,” she recalled. “We were just sitting there in silence. About two hours later, someone finally told us what was going on.”

Both officers were assigned to the Calumet district, and were working as partners when the incident occurred, the Chicago Tribune reported.

“Pray for the families of these two heroic young men, pray for the 5th District who, even tonight, will stop at nothing to safeguard the community,” Superintendent Johnson said.

Officer Marmolejo was a two-and-a-half-year veteran of the force, and leaves behind his wife and three young children, WLS reported.

Officer Gary had been with the department for 18 months, and leaves behind his wife and an infant.

“We’ve lost two young men, both fathers, young families,” Chicago Mayor Rahm Emanuel said. “This holiday will never be the same for those two families. While our hearts are with them, we lost people who answered the call to try and make Chicago a better place.”

A massive procession escorted the fallen officers’ bodies just before sunrise on Tuesday morning, the Chicago Sun Times reported.

“There are no words that can express the grief, the sense of loss,” Emanuel said, according to the Daily Herald. “It just knocks you back on your heels.”

“I think it’s really important that we put our arms around the Chicago Police Department and hold them up and support them at this critical juncture, because we are so dependent on their professionalism and their sense of duty,” the mayor added.