UPDATE: After reading this post my source contacted me and confirmed the accuracy of the transcripts. He was in the TOC shortly after the car bombing which precipitated this event and heard most of the calls live. The first call he heard was "Contact! Contact! Contact!" and subsequent calls stated they were taking fire from both uniformed Iraqi Police and shooters in civilian clothes as well. SAF is Small Arms Fire(again my source does not work for Blackwater)
The AP beat me by an hour or two but here is a look at the relevant part of the Blackwater radio logs on the day of the shootings in Nisour Square. They clearly show that the teams were either under fire or were dexterous enough to start creating a cover up while in the act of slaughtering innocents. I know which I believe. The log notes they came under fire shortly after entering the Square. A full look at the incident as detailed by my exclusive source is here.