According the LE they had the 3 guys under surveillance since they fingered the security guards. Arrest the guards but only watch the 3 guys that already said they were with her the night she disappeared. I'm not sure just when they actually talked to the three guys first.
"How can I arrest this young man (joran), he's the son of my best friend?"
Now, that statement I do buy.
Well, that's good at least. So the 3 were being watched from the beginning.
But if they covered their tracks right away, during that first night, before it was even noticed that she was gone, then it wouldn't matter if surveillance was going on.
I don't remember either when the 3 were first talked to, but seem to recall it was towards the end of that first week.