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CHICAGO — Two Chicago police officers struck and killed by a commuter train Monday night may have never heard it coming, according to experts and body cam video recovered at the scene.

Around 6 p.m. Monday, 5th District Officers Eduardo Marmolejo, 36,  and Conrad Gary, 31, chased a shooting suspect onto train tracks on the Far South Side, and were subsequently hit by a passing NICTD-Indiana South Shore train near 103rd Street and Cottage Grove Avenue.

A limited amount of body cam video recovered at the scene allowed investigators to shed some light on what went wrong. Marmolejo and Gary responded to the area after Shotspotter technology detected the sound of gunfire. After arriving on the scene, they followed a suspect up an embankment and onto an elevated section of southbound Metra tracks.

According to police spokesman Anthony Guglielmi, the video indicates the officers “clearly acknowledge” a northbound train headed in their direction while standing on the southbound tracks. However, they were apparently unaware of a southbound train bearing down on them from the opposite direction, moving at speeds in excess of 60 mph.

“They must have thought the sound they heard was the northbound train,” Guglielmi said. “They must have missed the sound of the train right behind them.”

Passing trains are supposed to dim their lights. Apparently one did, and the other did not.

Metra spokesman Michael Gillis said the transit agency was never notified that the officers were on the tracks, and since they handle dispatch at that location, they could not pass word on to the South Shore train operators that officers were on the tracks. Chicago police have called to ask Metra to stop or slow trains, he said, but that may not happen every time officers are near their tracks.

Transportation expert Professor Joe Schwieterman of DePaul University says it’s not shocking the officers didn’t hear the train coming, since there is a high density of train activity there. He says their sensory perceptions were likely limited as they focused on locating a suspect at night.

“The railroad route is quieter than usual because it’s electrical railroads, you don’t have the noise of the diesel locomotives; it’s also one of the busiest routes, with trains passing each other at a fairly high speed,” Schwieterman said.

An autopsy performed Tuesday indicated Mamolejo and Gary both died of “multiple injuries” after they were struck by the train.

CPD Supt. Eddie Johnson led a delegation of the department’s command staff to search the area along the tracks to recover the officers’ remains. Guglielmi said Johnson also met with the families of the two officers. Officers and firefighters lined the Dan Ryan as their bodies were taken to the Medical Examiner’s Office.

“These brave young men were consumed with identifying a potential threat,” Johnson said late Monday.

The man they were pursuing was taken into custody by other officers a short time later, and a gun was recovered near where the officers were struck. Police say a gun was recovered along with spent shell casings at the scene. Charges are expected soon, sources say, and could range from unauthorized use of a weapon to some form of murder charges.

The tragedy bears similarities to the 2002 death of Chicago Police Officer Benjamin Perez, who was fatally struck by a commuter train while conducting surveillance on narcotics activity on the city’s West Side.

Both officers were relatively new to CPD, Marmolejo serving for just over two years, while Gary had been on the force for 18 months. Officer Marmolejo leaves behind a wife and three young daughters, and Officer Gary a wife and six-month-old daughter.

Four Chicago police officers now have been killed in the line of duty this year, the highest number since five were killed in 2010.

“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,” Chicago Mayor Rahm Emanuel said Monday.

Organizations that support fallen officers and their family include the 100 Club, and GoFundMe pages have been set up for the families of both Gary and Marmolejo.