They planned the whole thing. Very clever. Not particularly elaborate but they must have known the risk enough to plan for and accept it. Unarmed protesters were allowed to tour the Capitol, and the media was set and ready to blow it out of proportion. They call it a deadly insurrection but the only deaths were by the police.

Also, it was totally obvious because even the Ellipse at the rally had higher security and snipers than the rear of the Capitol which had none. The front did though. Rear is where the weak police line fell back after marginal pushing by the crowd. Simple setup.