Many accounts were that people were being let into the building.

They went to recess for a few minutes and the stream was cut that's when there were reports of people entering the building.

The came back and resumed and started broadcasting again. But a minute or 2 layer, there were reports of shots being heard. This is where it went wrong.

The guy in a suit (probably SS) shot her.

If you watch the videos, there is another suit guy that starts helping and is talking to the cops behind her. She obviously was not a threat, or they would have been taking care of her. But instead some ass hat pulled the trigger.

This is why they panicked.

They feared actual riots would begin (they didn't.. for some reason) so they went into a lockdown prepared to defend form the backlash of the shooting.

Rioting didn't happen.

The next issue was they had blood on thier hands and needed to deflect blame.

So it turned into calling them terrorists to try to justify the murder.

Honestly, the people in the senate probably had minimal actual news of what was happening around them. They might honestly have thought there was a mob coming for them. They didn't seem to know about the protests getting to the door untill they were basically inside already