Is photo radar used for speed enforcement in any community on the west side of St. Louis?

Recently, I drove I-70 west from St. Louis. Somewhere near the airport a man on the right shoulder raised a hand held unit that appeared to flash, much like a camera. I then realized that he was wearing a very low profile, hard to notice uniform. Apparently, he was law enforcement. Within two miles, three police units were busy on the side of the road with traffic stops. Any ideas about what the flash unit was? Could it have been a type of speed enforcement? Could it result in a speeding summons in the mail?