I was going to agree with this, but then it sounded like you were saying they opened the glass window (either partially or fully) so they were throwing a rock at only the window and interior shutter... which doesn't explain the gathering of glass on the window sill.
The glass window had to have been closed didn't it? To have glass on the sill?
And if the issue is that there is glass inside a room instead of outside on the ground, then that means you only have two scenarios don't you?
1) That someone partially opened the exterior shutters, throwing a rock which struck the interior shutters causing a mark and embedded glass, causing the glass to fall onto the sill, into the room, but mostly in the area in front of the window.
2) Someone had the exterior shutters CLOSED, and partially opened the interior shutter, such that the rock struck the exterior shutters and ricocheted into the interior shutters, thus leaving glass only on the sill, at the foot of the window, and imbedded on the interior shutter.