This is a side issue....why does a twin not make 20+ miles from 7000' with some power left?
Based on the eyewitness accounts, shut down the wrong engine perhaps? If an engine was surging, it would be possible to misidentify the failed engine and it wouldn't be the first time.
What was the VIS like at the time? I get the feeling from the ATC tapes that there was at the very least haze, and more than likely fog/mist.