In the news conference the Sheriff stated that the Feds had an aircraft with "assets" (Stingray) that identified a phone in use in the area which helped them identify where he was located, probably to within a few feet.
This means they knew who he was from very early on and that there was only a single assailant. All of the law enforcement had photos of the assailant early on in the encounter.

He was a mentally ill violent liberal who had issues with his conservative family who had a restraining order against him.