There is plenty gap between sill and thing to use by hand to start raising shutter from outside. Raise by one finger thickness then put hand under shutter and raise to one arm thickness, slide window, use strap. No scratches, no damage. BTW shutter does not recess into sill - it sits on top of sloping sill. Hard physical evidence, missed by experts.
I'm not sure that I follow you on this bit.
This protrusion thing looks like a stopper and as it has a hole may also serve as a ventilation conduit. (Is there another one at the other end?)
So far ok.
But, if the blind had been fully down, I don't see where the finger space would be under the bottom of the blind.
Matt thought that some light was coming into the room - which might have indicated that the blind wasn't fully down (i.e. with spaces in between the slats), and possibly easier to lift slightly for finger space.
Alternatively, that protuberance could have been used to raise the shutter a little to give finger space.
If whoever lifted the blind had done so from inside, I don't understand why the strap wasn't used.
I'm not convinced that anyone entered via that window, but it's a possibility.