Casey's has recently bought many convenience stores in the area. The one nearest my house, on River Forest, was an All-Stop not long ago. The one in Elk Run, I believe was a


&Go recently. All the All-Stops in town, along with other gas stations, were recently taken over by Casey's, and undergone changes. I'd bet they have some kind of surveillance, but I'm not sure, and each store might be different. I know the one in Elk Run was recently remodeled (son's pre-school is nearby).
My point is that they had a hiring blitz, and you could apply at ANY location with the understanding that you may not be working at that same location.
I would suspect the FBI is looking for a receipt for something they may have as evidence - perhaps the energy drink cans, or cigarettes, or something else they may have found by the lake - that they will then attempt to tie to video or something. Or perhaps they've found something in a house or car or one of these neighborhood surprise raids, and are trying to see when/where/if it was purchased near the lake.