With gps they can locate you much more precisely than some of your application will indicate. Once they have the time, they are going to be able to capture every cell phone number within the tolerances of the the signal. So argument sake, at that time within a half block 13 phones were being used. They will take those phone numbers, and the carriers and begin connecting dots. First, they are going to find the date the phone was purchased, where it was purchased, and if it is a retail outlet, they are going to look at the video images, and most cellphone companies when they activate your phone have a time entered into their database.
They are going to seek a clear picture of the person purchasing the phone. I personally think they ran these checks yesterday, and came up against a dead end. A phone purchased online, another person buying the phone, or a transferred card to a similar phone which may be stolen from an innocent third party. Sophisticated folks are not going to get caught by the FBI because of phone records.....not going to happen.......less sophisticated folks are going to make mistakes.....using their own phones would have to be incredibly stupid. You steal a phone......the day before your operation, or better yet....just lift it.....take the card....put it back where you got it.....and give the phone to your operative who is going to set the bomb....the customer whose phone is not working is probably going to take a day to get to a store and get it corrected. My point is ......I think the FBI hit a roadblock, and the delay was going after those phone records.
Also, this kid who was on the front page of the NY Post could have been a planted photo to give them another day to trace the phones......they simply ran out of time and had to release their best evidence and get help from the public.