Two thoughts come to mind after watching the press conference:
1) these guys want the publicity this case brings. What other reason would there be for holding a press conference when they knew they could not answer any of the questions that the press was going to ask? A statement released to the AP and/or Reuters would have gotten the exact same information out to every member of the press.
2) The DA looked really ticked off and it got worse every time someone asked about whether or not the situation was handled in the best way. Making the arrest before anything was reviewed by the DA put him in a tight spot.
I didn't watch the press conference, but from what I have heard (no new info) I concur with number 1.