Well it was someone who obviously knew they were leaving for the UK next day so had to act quickly.
The Carpenters gave some useful information to the police, concerning what someone was saying whilst they were crossing the road outside the reception at between 9.15am and 9.30am, a voice was overheard calling out the name, 'Madeleine, Madeleine', which occurred after Gerry McCanns 9.05pm check, and Russel O'Brien and Matt Oldfields 9.30pm check! I find this a staggering piece of evidence, since it suggests that Madeleine might still have been alive by that stage! But rather more importantly, someone who knew Madeleine, and who Madeleine herself must also have known, was calling out Madeleine's name, twice!
Setting aside, all other scenarios for the time being, and now basing a new theorey on the strength of this previously unheard about testimony, we have someone who knew Madeleine talking to her at a pivotal moment that Thursday evening, between 9.15pm and 9.30pm...
It's possible, that this recognition of the name of Madeleine, and Madeleine being called out, coincided with the 9.30pm check made by Russell O'Brien and Matt Oldfield! This (if true) makes one or other, or both prime suspects involved in the disappearance of Madeleine McCann from the apartment (5A) that Thursday Evening!