The answer is pizzagate. They want him dead for exposing their vile nature.

I love how listening to Stewart/Oliver/Bee/Noah makes all of you think you are somehow affecting political trajectory on the world stage.

It also fits with the "right under your nose" detective's curse.

The killer is the asshole who was sitting in the mower outside of the school the first time they showed up (scar-faced and probably riding a John Deere).