This thing was a major police messup.
There should have been plenty riot police available that can force people to not enter. Obviously the risk of protesters trying to go in was high when Trump had a rally outside.
Not just a matter of doors sadly...
Felony murder applies when a person dies while the offender is committing any of a set of felonies. It doesn't matter how the person died, or whether it was intentional because the intent to commit the initial felony is enough.
The canonical example is everyone who took part in a bank robbery can be charged with murder if the bank guards kill one of the robbers. This even applies to the getaway driver, who may not have entered the bank.
The initial felony could be any of: the assault on the building, breaking & entering, various domestic terror statutes we have for this sort of thing.
There were at least 4 deaths at the Capitol yesterday. All of the insurgents should be facing 4 murder charges, in addition to the other charges that we would expect.
Edit: possibly relevant statute: https://code.dccouncil.us/dc/council/code/sections/22-2101.h...
This appears to indicate that everyone who illegally entered the Capitol yesterday can be indicted for first-degree murder, which carries a sentence of 30 to life in DC.
The opposite sends the message that you run a low probability of sanction if you attack the US Capitol. Very bad incentive.