With the disclaimer that I've heard about but never actually heard Murrow's broadcasts from London, I that the same function as was performed by Murrow's broadcasts ("eyewitness testimony to a tragic event," to borrow your words) has been more than adequately performed by the hours of broadcasts made from the bridge immediately after the collapse. Broadcasting the 911 tapes now, 3-1/2 weeks out from the event, reeks (to me) of trying to drag extra life out of an old news story. YMMV.