Some of you guys have an inordinate capacity for suspension of disbelief. I like the DV as much as anyone, but good grief. A plot hole is a plot hole.
You guys are attributing the US government with plot power comparable to ministry of magic in Harry Potter. And the other half of you is giving human rationalization totally unrealistic capabilities. It doesn't work this way IRL.
Note I'm not saying the cat is totally of the bag here. But people would absolutely, totally, completely certainly, without a doubt, indubitably, know that something strange happened. They may not know what kind of animals attacked them. They may not even think it was magic. But its crazy to say that the general facts of the incident would not be known. Not. Possible.
But I digress. I am sure Jim will explain everything all in due time, one way or another.
This is not something new. People has known all along.
Who have not heard of strange supernatural happenings?
That is that creepy house over there. That particular small town is spooky. There are strange sounds in that neighbourhood at night and so on.
People know, but nobody really investigates and do something about what they know or suspect. They don't even talk about it. The majority pretends they do not know even if they do, and try to forget the stuff ASAP. Rudolph's strong denial is just an extreme, but most people in the DV is like that to an extent.
Out of sight, out of mind. And I suspect in the hindbrain of your average humankind lurks the fear of supernatural so deep that it subconsciously urge humanity away from all things supernatural as a survival mechanism. Much like the fear of the darkness. You need a strong act of will to resist this aversion, at least in the beginning until one manage to adapt. Most of the time the adaptation process is rather painful at best and deadly at worse.
As long as the supernatural does not flaunt themselves in broad daylight and force vanilla mortals to a corner, most vanilla are only too happy to let things be. So yes, even if there are clues left behind, the attack in changes will be covered up. The supernatural has been leaving clues behind for any willing vanilla all this time, but very very few actually follow the thread. In Harry's almost 20 years of wizarding career, only Murphy, Susan, Marcone, the alphas and possibly Hendricks and Valmont whom willingly and knowingly jump into the pool that is the supernatural world. Not very many, Butters does not count, because he is dragged into it kicking and screaming. The others, like the Carpenter family are rather supernatural themselves and are already involved in this world to begin with.
A Vanilla capacity for denial is extremely powerful in the DV.
The others, like Rawlins, Micky Mallone and the SI people knows spooky stuff exist, but they kept quiet about it. . I think very very few vanilla truly ignorant about the supernatural. Knowing is one thing, acknowledging it however is another matter.