I don't know about Mena, or why Delta was there, but they were there.
The best site for this type of info is Carol Valentine's Waco Holocaust Electronic Museum.
You'll also find that's the only site with the complete autopsy reports. (WARNING: Very Graphic --not for the squeamish)
Search for Koresh and Mena on these sights:
http://www.mindcontrolforums.com/pro-freedom.co.uk/report_on_waco.html
http://www.rumormillnews.com/wilcher.htm