Sounds very plausible. Where were his 2 younger brothers during all this toing and froing? With their mother or asleep at home? Has anyone asked them about their brother's coming and going? Was Joran a HS junior or senior, and if the latter, did he attend graduation ceremony?
I dont know if the two younger Van der Sloots were on the trip to Holland or not. If they were home...well, maybe they are sound sleepers.
Joran did take his final exams and graduate before his arrest.