By Marissa Parra

CHICAGO (CBS) — The FBI and Metra Police Department are asking for help identifying the gunman who opened fire with a collapsible rifle on the McCormick Place platform last week.

As CBS 2’s Marissa Parra reported Wednesday, the FBI released startling video Wednesday of the man, who had just stepped off a train when he fired the rifle.

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Around 10:20 a.m. on Dec. 1, a man got off a northbound Metra Electric District train at the McCormick Place station, pulled out a collapsible rifle from his backpack, and fired a single shot while standing on the platform, according to the FBI and Metra Police.

(Source: FBI)

It was unclear who or what he might have been shooting at, but no one was injured.

Sources told Parra the man entered the Metra Electric line at the Museum Campus stop in Grant Park, a short distance north of where he went on to hop off and fire the rifle.

Video showed the man stumbling his way onto the train at 11th Street and Michigan Avenue. As the mystery man gets off the train at McCormick Place, the stumbling continues.

“When you watch the video, you do see that this individual does have an unusual gait,” said FBI public affairs officer Special Agent Siobhan Johnson. “We’d look at that gait and say that perhaps it’s possible this person was under the influence of some type of substance.”

Johnson is one of many with the FBI who have spent hours poring over the details of the videos.

They are trying to understand what happened after the moment when the man stopped by the stairs at the McCormick Place station, pulled out that rifle from his backpack, assembled it, and fired the shot.

It was unclear who or what he might have been shooting at, but no one was injured.

The man then placed the rifle back into his bag and exited the station. Chicago Police and Metra Police searched the area for the gunman, but could not find him.

(Source: FBI)

The million-dollar question is why.

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Johnson said there is a possibility that it was all planned – a small moment meant to be a larger moment.

Another possibility, she said, is that “it could be just an opportunity and there was a significant error in judgment – they just got the idea spontaneously to do it, or perhaps they were under the influence.”

The FBI on Wednesday was still looking into what type of gun was involved. They know it is a rifle that was collapsible and small enough to fit into a backpack.

But since we don’t know anything about the man, we don’t know if he had any special concealed carry permits that would make carrying the rifle legal.

But choosing to fire the gun in public the way he did is not legal for anybody – even with no one around.

Luckily for the FBI, he did it in front of cameras. Images showed a man with close-cropped hair and a receding hairline.

“I mean, he has a beard that’s visible. You can see his eyes very cleanly,” Johnson said. “If you know him, you know him.”

The man appeared to have a mask down on his chin. But Johnson said it would not be a hindrance in finding him if he had been wearing the mask over his face.

“When you walk through the city, you leave a huge trail digitally,” she said, “and with respect to people that you meet, we’ll find you. It’s just a matter of time.”

The FBI said the man should be considered armed and dangerous.

Anyone who recognizes him can call the FBI at 1-800-CALL-FBI, or report him at tips.fbi.gov. Anonymous tips also can be reported to Metra Police at (312) 322-2800 or via their “Metra COPS” app available for mobile devices.

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