I can't understand the argument that IF Guede was the lone assaulter/killer, then it wouldn't have been logical for him to lock the door - especially when set against the logical reasons offered as to why AK/RS would have benefited from locking the door if they'd been involved.
There are very many sound reasons why Guede would have wanted to delay the discovery of the body for as long as possible (if he were the lone attacker). Here are three of the biggest ones:
1) It would have given him far more time to be seen acting "normally" around town - thus establishing a pattern of behaviour that Guede could rationally have thought might later work in his favour (i.e. "How could I be her killer? I was dancing and chatting totally normally into the small hours of the morning!". NB: Clearly, Guede would have known that he had no alibi for the time of the murder (given that he was the killer), so maybe he'd have thought that this "post-crime alibi" was the next best thing.
2) Delaying discovery of the body by locking the door would have been a viable way (as Guede might logically have thought) to maximise degradation of evidence within the room, thereby possibly making it harder (in his mind) for police to find usable evidence of his presence.
3) Perhaps more significantly, Guede might have reasoned that a lengthy delay in the discovery of the body might make it very difficult to determine with accuracy a time of death. This would dovetail in with reason (1) above, since suddenly Guede's very visible behaviour in the early hours of the 2nd November could also be seen as an attempt to actively construct a time-of-murder alibi if Guede hoped the time of death would be ruled indeterminate.
In addition to these case-specific reasons, I think it's fairly well-established that most murderers (but often, interestingly, not serial killers, who routinely harbour a strange desire to get caught) actively try to hide (or delay discovery of) their victims - if they have the opportunity to do so. To me - in addition to the more specific reasons I've given above - this applies equally to Guede acting on his own (as, incidentally, it would also apply to a RG/AK/RS combo).