That's not a big mystery. Rather a Nebelkerze. The NYT wrote this about the murder, at
https://www.nytimes.com/2021/01/08/us/brian-sicknick-police-...:
> Law enforcement officials initially said Mr. Sicknick was struck with a fire extinguisher, but weeks later, police sources and investigators were at odds over whether he was hit. Medical experts have said he did not die of blunt force trauma, according to one law enforcement official. “He returned to his division office and collapsed,” the Capitol Police said in the statement. “He was taken to a local hospital, where he succumbed to his injuries.”
As horrible as that is, uncertainty of how it happened is to be expected in such a chaos.
More interesting: Why weren't the officials on the radio, why are there videos out there of police letting rioters in directly in front of the capitol, why was there no support, why wasn't the intelligence about the impending terrorist attack shared? Was an armed response even considered?
The corruption is completely obvious and evident, only incompetence can explain parts of it away. The article shines a light on what happened that day and covers those thoughts, that makes it interesting.