In his book Madeleine - The Truth of the Lie, Goncalo Amaral writes of the difficulties and trials the Portuguese police faced when they attempted to collect forensic evidence. In particular, he writes...
Lots of people were already in place; however, nobody appeared in the photos. We don't know, for example, how they were dressed. Such observations can turn out to be important later on. The report mentions that the twins were asleep in their bed, but there is no proof to confirm it; on the contrary, in the photographs, you can see empty cots, where only the mattresses remain - the sheets and blankets having been removed. Why have their beds been stripped? If the sheets had not been removed, traces of their presence could have been found there.
The search and examination of the scene were carried out in difficult conditions: when they arrived, the police were met with a large number of people coming and going - family, friends, resort employees, including dogs and members of the National Guard. The contamination of the premises risks bringing serious prejudice, as a consequence, to the investigation. We must ask ourselves if that contamination has been deliberate or not - it can make the search for clues particularly complicated.
Inside the apartment, police forensic specialists proceed to lift finger and palmar prints, a job that is preferably carried out during daylight hours. Others look for traces of blood, samples of fibres and hair. We notice with dismay that one of the technicians, who is working on the outside of the McCann children's bedroom window is not using the regulation suit, thus risking contaminating possible clues. These images of negligence start to circulate world-wide; this isn't, however, the usual behaviour of police judiciaire technicians. It's obvious that no one has broken in and the lock has not been forced. No prints are lifted that are likely to belong to an unknown person, nor the slightest trace of gloves which could have been worn by a hypothetical abductor. In the middle of this desert of clues, two prints are perfectly easily found: the very distinct mark of a palm print on the balcony window at the rear of the apartment, and a clearly visible one of fingers on the window pane of Madeleine's bedroom. The excellent quality of the palm print seemed suspicious to us. Later, analyses confirm our suspicions: it belonged to one of the officers who were present the previous night.
Could more have been done to preserve a potential crime scene?