The police on Ashli's side of the doors stood by doing nothing as the windows were broken, then withdrew from the area near them. That gave Ashli a reasonable expectation that she'd be allowed to proceed without being in danger, only to be shot treacherously from the side.
John Sullivan, who made the video from the left, saw the drawn gun of the policeman on the other side, and before Ashli climbed into the window yelled "He's got a gun." It was so noisy, though, that in another video he says he's sure she didn't hear his warning. Also no warning can be heard in the video taken from Ashli's side of the hall, and the policemen on her side didn't act as if they knew there was someone on the other side with a drawn gun.
Ashli climbed up into the window looking straight ahead, and was shot immediately -- in effect, from ambush -- by the shooter on the other side, to the left of the doors. I don't think she ever realized he was there.
Here are videos taken from the right and left of the hall. (I recommend that these be saved before they are taken down, especially the one from the right, which shows how many police were there, and -- at the time Ashli was shot -- the nearly empty hall all the way down to the open door at the far end, which gave easy access for evacuation to anyone who wished to leave). No one was in imminent danger, and the shooting was not justified:
“I’m from the Government and I’m here to help.”