IMO access via a key is entirely plausible, although it is one of a small number of plausible theories.
In this scenario the window may be a distraction; perhaps opening the window/shutters was intended to draw attention away from the use of a key to gain access, or to give the impression that Madeleine had climbed out the window and wandered off, in order to buy time/confuse.
But I believe, from the evidence in the files, that it is "almost certain" (to use SY terminology) that MBM disappeared from the apartment after the MO check around 9:30 (providing parental involvement is ruled out).
This would only require minor modifications to Sadie's theory, in that JT could have potentially seen an abductor when she went change places with ROB after her main meal.
It is a pity the statement from Crecheman is not available, which may help refine what JT may or may not have seen.
All IMO.
It has always been a mystery why Gerry thought that his chat with Jez took place towards the east side of Rua Francisco G M. [Cutting Edge video]
A part of my mini theory, which I missede out, is that Gerry and Jez were chatting in the road towards its eastern pavement .... and that a vehicle coming made them back away to the spot where Jane saw them and which both Jez and Amaral confirm. If that vehicle was the getaway vehicle, seems it maybe dithered then changed ditrection upon seeing Gerry and Jez (and Jane) and then hot fotted it in a Southerly direction.
I full accept that this may not be the case but it is a distinct possibility and would account for Gerrys mistake about which side of the road they standing on when chatting. It could, of course, have been another vehicle passing by that caused them to retreat to the western kerb by the alleyway
BUT when I was there mid summer (June IIRC) 2010 there was a dearth of traffic along that road, either motorised or walking, day or evening. We didn't bother with the pavements, we walked in the road it was so quiet.
This tends to point to the earlier time that Jane walked that walk, rather than the later time.
But we dont know for certain, do we?