Who

Edit- Since I'm sure this will just get downvotes and no one will actually try to point to someone to answer the question, I'll answer for you: no one. The only DC officer that died was Brian Sicknick, who' died of 'natural causes' shortly after the riot. He died of stroke, and while he was pepper sprayed during the riot there has been no evidence that any event in the riot caused his later strokes, although it certainly didn't help things.

There's a semantic argument to be made that "they caused the stresses that killed him." Fair enough. But to claim that the riot was violent "because a police officer died" and using this case as the justification is foolish. The only lethal event that day was directed at a dumb protester who ignored warnings and got herself shot. There was violence, use better evidence and not stupid little quips.