Dave Underwood was murdered by a "boogaloo" terrorist. The boogers were hoping that, by targeting police, they could escalate the existing BLM protests into a civil war. Officer Underwood's murderer was supported both before and after the crime by a small cell of boogers, including a pedophile who was plotting to frame Antifa for booger attacks.
As you may notice by the lack of a civil war, the boogers were less than successful.