That's what I'm asking.
I'll play devil's advocate.
1. The window being open is nonsensical.
2. Dogs woofing in the apartment.
3. The timeframe was extremely tight if you are following SY's Crimewatch timeline.
4. These types of abductions are extremley rare in Portugal. At least the available statistics seems to indicate this.
5. There would be easier children to snatch. Especially if you knew the parents/friends were back and forth and often as they say they were and an abductor was watching.
6. It is statistically speaking usually a family member or a close friend or someone who knew the child who is responsible.
Just some reasons off the top of my head. The trouble with this case is with no real clues how can we know? Sure I can imagine an opportunistic abductor darting in or opening the window and coaxing the girl over. It's happened before. I do agree that with the parents that dunnit angle it's hard to imagine how it could be done.