FAQ for
[Rec] (2007) More at IMDbPro »

The girl in the penthouse is Tristana Medeiros, who was seen in the newspaper clippings that Angela and Pablo discover while inside.

The former resident of the penthouse was an agent of the Vatican who was charged with researching and isolating a suspected virus believed to be the biological cause of what was described as 'demonic possession', which was later confirmed to exist in a young girl (Niña). The agent kidnapped and brought the girl to the penthouse to conduct his research and to possibly cure her; unfortunately, during the work the virus managed to mutate and become contagious. The agent abandoned his efforts to cure her after failing to engineer a vaccine and sealed her in the room before leaving the city.

How the virus spread from then on - and the origins of the boy in the attic, remain unclear.

I believe the person in the penthouse is in fact the priest/vatican envoy? - No, it's Tristana Medeiros.

And what looks to be a boy in the attic is actually the possessed girl.

- No, it's a boy of unknown origin, probably used in the experiments done by vaticant agent. He plays important role in REC 2.

The priest in trying to cure the possession by physical means inadvertantly created a type of possession virus which he in turn caught and sealed himself in the apartment while perhapse sealing her in the attic knowing that if this got out it could mean the end of the world.

- No, he did not get diseased. But why he sealed her instead of killing her and removing evidences is still uknown. But his presence in the building is actually possible (despite what was said, that the owner of the attic was not seen for years) - new stills from REC 2 show unknown man and Angela alive - so perhaps he indeed was hiding in the apartment opposite to Tristana Medeiros and pulled her back.

In the bonus features of the DVD it is shown that the person in the penthouse is based on a drawing of an older man. - It's the real actor.

As for the spread of the virus it is possible that the priest and the girl were eating rats that the priest was using for experiments to find a vaccine and the rats spread the infection. - One of the possible ideas.