Creepy: a warning to the online world

My husband participates in an online discussion board for his favorite game, Heroscape. He has developed friendships with people from the site and has invited a couple of them over to the house to play. One of the guys he invited over struck me as a bit creepy. Hubby told me he was harmless, just one of those 'weird characters' you meet sometimes. Still, I was happy I had insisted beforehand that someone we had never met was not spending the night in our home. If it was just the hubby and I, that might be different, but I will not do anything to put my daughter in possible danger.
So, it has come to our attention that this guy, let's call him UD, is possibly a child predator. One of the guys from the discussion board went out of town for a week, and came back to find that UD had made contact online with his 16 year old daughter. Apparently there were many emails, IM's, etc in which UD told the girl, among other things, he loved her and wanted to fly to her state to meet her. Asked for information on hotels. From what I understand, sex was not mentioned, but was obviously something on his mind. Why else would a 27 year old married man with 2 children solicit a 16 year old girl online? The girls father is thankfully a responsible parent who monitors his childrens online activity. When he came home, he reviewed her accounts and discovered the emails, and then went further to view her IM's and stuff. Thank God he found this out in time. The authorities have been contacted. Unfortunately, they say since nothing actually happened (ie the meeting never took place) and sex was not explicitly mentioned, that all they can do is put him on their list of possible threats and keep an eye on him. I have not seen these emails or anything myself, but we have it from good authority (a friend who is a cop, who is, ironically, on the same discussion board, and has become involved in the case) that it is definitely the work of someone wanting to solicit a child. Even the girl, upon reviewing everything, was glad that her father had found out because in hindsight she saw that it was not right. She wanted to bait UD so that the police could catch him but they did not want to use her as bait.
This totally creeps me out. This guy was in my home. My daughter had contact with him. Granted, she is 2 and this other girl is 16, but in my opinion this doesn't matter. A sexual predator was in the same room as my daughter. I am totally creeped out. I hope that he does not remember how to get to my house. I hope that the authorities find some reason to arrest him. I cannot believe that nothing can be done at this point. This man's wife is in the military and they are based a couple of hours from here. He has access to military bases and people let their guard down on base. You assume you can trust other military people. I can only assume that military children would be more likely to accept a ride or something from a stranger on a military base because you assume you can trust these people. I hope that this is an isolated incident with this guy and that nothing worse is done or has been done. I hope that noone else has to suffer the fear that this girl and her family have been subjected to.
Let this serve as a reminder to us to use caution in our dealings online. If you have children, please monitor their online activity. This is not an invasion of privacy, this is responsible parenting. Children (yes, even 16 and 17 year olds) are very impressionable. They are flattered by the attentions of an older man (or woman) and are naive enough to think that nothing bad can happen to them, that they know what they are doing. In reality, these predators know what they are doing and will do and say whatever is necessary to get what they want. And sometimes what they want is your child. Be aware and take the necessary precautions to ensure this does not happen to your family.