Atta's and Binalshibh's movements in the area were first detailed by the Spanish newspaper El Pais.
No Vacancies
According to Pere Gomez, the hotel manager, the receptionist on duty declined to rent them a room, despite vacancies, because she didn't like the look of Binalshibh; the other man stayed in the car and the receptionist did not get a clear view of him, the hotel manager said. The two drove off to the nearby Hotel Tropicana, which was full but whose receptionist offered to call other hotels to find the pair a room. She located a double room -- back at the Hotel Monica.
The Hotel Monica?
Unfortunately, it seems like only the Washington Post and New York Times have the staff depth and knowledge base to routinely do this type of reporting. I know there are a few others for the news magazines and the WashTimes, but it seems like the WP and NYT routinely have articles like this.
Which raises the point - how do the reporters obtain this information. Digging through the Spanish police reports? Probably getting to know the police folks in Spain, plus having government contacts ("US officials"). Sources are sources, and sources often have agenda.
And the other issue in my mind is - how reliable is this report? What spin does the reporter put on it - it seems pretty factual to me, not biased one way or another.