More than just the audio tapes is needed. If they use CAD (Computer Assisted Dispatching) and many departments do these days, there will be something called a chronology that is a text record of all info entered into the dispatch console along with all messaging between the dispatcher and a "call taker", provided they use "call takers", who actually take the 911 calls and type in info which is IM'd to the actual dispatch - sounds inefficient but some departments do it that way. The chronology will have a running text of the event until the call is closed out. Get ahold of that and it's another piece that can be examined.