Every time we start talking about the DPD I picture Barney Fife. He would have done a better job. They seem to have no professional chain of evidence, promptness of investigation or ability to read caller id. My dad would have called it a Chicken Sh*t outfit.
I think part of it depends on their 911 system. I'm pretty sure they have to request a gps location on a 911 call which signals the towers to do the search.
On most camera type phones, when you take a picture, I think the tower information is embedded in the file metadata. But, I'm pretty sure that each call does not trap gps data on the cell phone itself for normal cell calls. Although I'm pretty sure a subpoena could capture at least the tower information from the provider.