As described, it sounded like they launched their investigation into massive bribery and 'pay-to-play' in the County by implementing Pen Register on selected politicians they thought might be involved and recording the phone number information of every call they made over many months and then used processes such as reverse dial-up to identify the phone numbers called and used that (meta data) to justify requesting court orders for multiple wire taps.
The taps were installed and then monitored for 9 months and the results gained were used to convict a number of
While searching the tubes for more information about Pen Register I found a fascinating quote on the process but then realized that the source was a leaked document put on the web by the Guardian after they got it from Snowden and not a formally released document. Oh well. We don't use leaked documents around here.
It was a fascinating talk this evening and just one of many we heard tonight.