Now, this is what is wierd. Each phone has a certain serial number/tracking number/some kind of number....I know this bc one day I called my provider from my burner phone to report that my other smart phone was not working and the agent could tell exactly which model burner phone I was calling from...it was a cheapo prepaid at the convenience store and he knew all of its specs. This came up bc he referred to repairing that model when in fact I was calling about another phone. It was like caller ID...I guess not only my number came up, but also the type of phone I was calling from!
So, I've been thinking about this. They might have been at least able to find out what phone, where it was purchased, and when via its serial/tracking number..now, whether or not the outlet would still have any information/surveillance footage of the buyer is another story...
or if we are dealing with street thugs, it could have been bought/obtained on the street, literally...
Here's another angle on this. If they were able to determine that it was a burner phone, which they have, they have likely gotten warrants for all the activity on that number...so if the "seller" contacted anyone else with this same phone, that would be evident in the call logs of that particular number. So, maybe LE is talking with other people who might have been potentially contacted by this "seller(s)". ETA: It would also be a lucky break if the "seller" used this same phone to call someone who could be connected to him/her, say an accomplice, friend, family member, work, etc.