Deputy Blake Gruny arrived on the scene and spoke with the employees, who said they called authorities because they were unsure of whether they should just throw the carcass in the trash.
"I observed a dead shark approximately 4 to 5 feet long in a shopping cart," Gruny wrote in his report.
He wrote the shark was found in a "suspicious circumstance."
Gruny said surveillance tapes from the parking lot didn't reach the area where the shark was apparently dumped, so he contacted the owner of the RV.
The RV owner said he had been parked in the Walmart lot overnight and he heard a loud noise about 7:30 a.m., but thought it was just Walmart workers collecting stray shopping carts.
The man said he left the RV to go to work and discovered the shark had been dumped on the hood of the vehicle. The man, a West Virginia native, said he removed the shark from the vehicle and went to work.
The investigation is ongoing. The carcass was removed for disposal by the Florida Fish and Wildlife Conservation Commission.
Dr. Jim Gelsleichter, an associate professor of biology at the University of North Florida, said the shark appears to be a blacktip or spinner shark. He said both types of shark are common in Florida.
"But in the Walmart parking lot, that's a bit uncommon," Gelsleichter told WJXT-TV.
The sheriff's office said a second mysterious dead shark was found the same day in the driveway of a North Beach home.
