He came back a few hours later -- and that's when it got strange.
"The suspect or offender walks around and eventually hides behind a display at the front wall of the business," Robertson said.
Deputies say the man hid behind the display sign for nearly five hours waiting for the store to clear out and close up.
Video shows him come out of hiding, smash a glass display case and grab handfuls of jewelry.
He got away with more than $13,000 worth of jewels.
Deputies believe surveillance cameras from a nearby theater captured the truck the man used to get to and from the Costco. They're confident someone will recognize the man and turn him in.
Anyone who recognizes the car or the thief is urged to call deputies. Investigators are still working to figure out if there are other suspects in the case.
Customers said the fact that he got away with it is unsettling.
"It think it's really shocking and scary," Hilerin Gordon said. "How did he get away with it?"