A moment of panic.
The bullet holes in the glass appeared to be about two meters off the ground, and the impact points on the bookshelf were a little over two meters high. At first glance, there was almost no difference in elevation between the two bullet impact points.
Assessing the bullet trajectory's primary function was to determine where the bullet came from, and it could even roughly deduce the shooter's position.
The bullet hole in the window was two meters above the ground, which was quite high. Even if someone raised their gun above their head to shoot, the glass would not have been hit at this height first. So if the bullet had been fired from outside the window, or very close by, there should have been a noticeable change in the bullet's path.
