But were any reported missing?
Did the police investigate this possibility? If they didn't, it was a huge omission.
We don't know, but it is a v ery reasonable speculation that a key was acquired and thus the front door used to gain entry and exit.
I don't know if the police did, they certainly should have done in the early days, that is for sure.
(See! Whilst not a believer in the abduction theory i have no issue in actually stating what the police did or didn't do and whether it was right or wrong!)
I disagree though regarding it being "a very reasonable speculation" as no one has ever come forward to say there key was stolen, lost, borrowed or missing.
No locksmith has ever come forward to say he cut a key that matched that one.
Certainly given the media exposure of the case you would think had someone any knowledge of their key going missing or of someone cutting a key like that then they would have come forward in the intervening years.
So that means you are relying on an inside job from someone with access to the key and an inside job on a locksmith.
We also have to look at the probability of someone having the very key to the very apartment that a child was staying and was left unattended. That is a huge coincidence!
Why not any of the other apartments where the children weren't being left? Another huge coincidence!
And then it's a what point do you accept huge coincidences become at best, unlikely, or at worst, impossible?