The video shows a car pulling up to an armored truck just outside the Country Club Hills store, and immediately get into an exchange of gunfire with guards from the armored truck.
This happened Monday.
The Walmart reopened the next day.
It's believed one of the suspects was shot before they carjacked a customer and got away.
A $20,000 reward is now being offered for an arrest and conviction.
Country Club Hills police said officers responded to 4405 W. 168th Place for reports of an active shooter just before 10:30 a.m.
FBI gives update after Country Club Hills incident
Armored truck personnel were conducting business at the Walmart there, and that's when a sedan pulled up, an FBI spokesperson said.
There was an exchange of gunfire between the armored truck personnel, a Walmart security guard and the would-be robbers, police said.
The suspects then crashed their sedan, got out and carjacked an "elderly person" before fleeing the scene in their vehicle, an FBI spokesperson said.
An FBI official also said agents had responded to a bank robbery at a U.S. Bank, located at 4350 Lincoln Hwy. in Matteson, minutes earlier.
Shots were fired in that incident, and no injuries were reported, the FBI said. It was not immediately clear if the incidents were connected.
This is at least the fourth robbery or attempted robbery of an armored vehicle in the south suburbs in the last month and a half.
ABC7 Law Enforcement Expert Ed Farrell said the crimes appear to be an escalation of a recent pattern of street robberies by teams of suspects.
"It's a direct threat to public safety, not only from the security guards, but it's a Walmart parking lot. There's people and patrons coming in and out of there," Farrell said.
The FBI said they are reviewing them to see if they are connected.