He was well-funded and looked like a strong candidate out of the gate. Plus they wanted Kunzweiller out because he charged Betty Shelby with a crime.
That, and Kunzweiller was saddled with prosecuting a Tulsa Police officer who used department computers and resources to stalk his daughter's boyfriend. Up to that point the D.A. had done everything the union wanted, but expecting him to ignore a high-profile killing like that was just unrealistic. (new topic?)
https://www.washingtonpost.com/news/morning-mix/wp/2017/10/19/white-ex-tulsa-police-officer-convicted-of-fatally-shooting-daughters-black-boyfriendAs for the LED billboard: The couple killed at that intersection yesterday evening making a left turn from 41st onto Yale would have certainly seen the bright, oversized billboard in their peripheral. If it were playing video it could have caught their attention at the worse possible time, but we have no idea whether or not it played a role in the deadly crash.