This sounds like something the investigations of the Jan. 6 attack on the U.S. Capitol should be taking a very close look at: Most of the ground-floor windows and doors in the Capitol had been reinforced just a couple years ago. But the insurrectionists were in several cases able to zero in on the dozen or so ground-floor windows and doors that hadn’t been reinforced, the Los Angeles Times reports.

Most of the building’s ground floor had been strengthened in a 2017-2019 renovation, with the view that the biggest threat the Capitol was likely to face came from a bomb outside of the building, and a large risk to human life would come from flying glass. A few windows weren’t reinforced either because they were seen as unlikely to pose an implosion risk or because the heavier frames of bomb-proof glass couldn’t be supported by specific parts of the old building. They were left reinforced only by thin Kevlar film added after 9/11.

The reasons for the choices about reinforcing or not reinforcing any given window are worth revisiting, and maybe the security improvements made to the Capitol in the wake of Jan. 6 will bring shifts. But here’s the most interesting part: How did the insurrectionists find the windows and doors they could batter their way through?

“Video shows some of the first rioters to break through the police line running past 15 reinforced windows, making a beeline for a recessed area on the Senate side of the building, where two unreinforced windows and two doors with unreinforced glass were all that stood between them and hallways leading to lawmakers inside who had not begun to evacuate,” the L.A. Times reports. 

That took effort: “The four unreinforced windows and doors that were the first points of entry on Jan. 6 are all in a recessed alcove, shielded by exterior walls on three sides. They were not the first windows, nor the easiest to reach for rioters storming up the Capitol steps. Attackers ran more than 100 feet across a courtyard to reach the covered outdoor entryway, where two unreinforced windows and one of the doors are.”

It sounds like at least some people in that mob knew where they were going and what they were doing in targeting those specific entries. So … if that’s the case, how did they know? This is something to investigate.

Did the mob just get really lucky? 

Or had some part of the mob—say, some Proud Boys or Oath Keepers—carefully observed the Capitol’s defenses in advance, then led the rest of the crowd to those places? That could really juice the level of conspiracy understood to have been at play.

Or, worse, did they have inside information? And if so, who provided it?