I will admit that I was not there to witness this firsthand, but I heard several corroborating stories, and I then saw it on the surveillance camera footage.
Last night, a customer came up to the floor associate and asked to get a tablet and a pair of high-dollar headphones. No problem. She unlocks the cases for both items, and carries them up to the register for him, as per procedure. She leaves the items with the associate on the register (lets call her Sunshine), and goes back out on the floor.
When the customer gets to the register, he starts mumbling incoherently to Sunshine about color choices for the headphones and other things. Now, the store is pretty busy and the line is backing up.
The second cashier for the evening (we'll call him Lanky) comes out of the office to get on his register, and Sunshine takes the opportunity to hand the customer off to him so that she can attend to her other customers.
Once he is out of Sunshine's earshot, the customer's story changes. He is now claiming that his sister bought him both items and that he was dissatisfied with the color of the headphones and wants to exchange them. He asks Lanky if there are any other color options for them, and on being told "no", the customer thanks Lanky for the help and walks out with both items.
No security devices on them to trigger the sensors since they had been under lock and key. Lanky had no idea that the customer's story wasn't true. Granted, Sunshine should have told Lanky the story beforehand, but her line was seriously backed up and she is the sort to want to think the best of everyone, so I'm not surprised she didn't think of it.
It's not often that someone gets to just waltz out of a store with over $500 worth of merchandise, in plain view of two associates.