You should probably grind the melted platters into a fine dust and mix it into moist catfood. Then spread the catfood around town for feral cat's to ingest. Then track down the cat scat and burn it. Capture the smoke and save the ashes. It's the only way to be sure.
If you take your computer to Best Buy for service, you deserve what you get.
I agree with the Worst Buy part. Now as to the hard drive destruction thats probably not quite good enough. Nuking it from orbit is really the only way to be sure. But if you want some extra insurance nuke it from orbit and then do that if you can find the pieces...