Possibly a ring of perps preying on tourists with date rape drugs for after hours parties
I read a post a while back, either on this site or one of the several others that I've been reading, that said that the way it works is the local guys will befriend the tourist girls and find out when they're leaving.
Then the last night the girls/women are there is the night they are given the drug, and assaulted, presumably because if they're leaving the next day, they're less likely to want to pursue charges.