Had they simply been 'casing the joint' for a burglary which was carried out, there would have been no witnesses for the simple reason a burglary would not have been reported in the media.
Perhaps having done the groundwork it was realised there was a very valuable commodity in the apartment. If phone calls were made in the run up to the 3rd the significance would have been missed as the only phone traffic forensically examined (there's that word again) was the traffic between the prime suspects.
The initial intention of burglary (two adjacent apartments had been broken into) could easily have changed to targeted abduction.
I can't exclude a targeted abduction, either. So far, I haven't found anything to substantiate the "abducted-to-order" scenario involving several people.
Could an individual have seen M and "flashed" on her. Yes, why not?
Could a burglary have been an excuse to involve an accomplice? Possibly.
Could someone have decided that she resembled a descendant (or relative) of some historical figure and needed to be "rescued"? Possibly. Were all sects checked out?
ETA: Were any "communities" ever checked out?