I mean no offence to anyone and don't wish to upset the thread. However, I do find all these questions about LE or FBI did or didn't do slightly irritating. If you are part of LE or FBI, of course, you are going to enhance and get the best photo available, Of course, you are going to do voice recognition and accent, dialect, of course, you are going to do profiling, of course, you are going to do the internet, phone traffic investigations and of course you are only going to ask the General Public for the information you need. Asking for enhanced photographs is as much use as a chocolate fire guard, FBI LE have already done it and asked the General Public for help.
What may help is the voice was analyzed where was it thought to have originated from? (That may ring a bell with someone somewhere)
Sorry to sound off no offence meant to anyone I am sure LE/FBI have done all the obvious.
Cheers
Reacher