My question involves criminal law for the state of: TN

Someone had hacked a friends facebook and posted a criminal threat on her profile. Then someone concerned turned it into the local police. 11 days after it was "discovered" by police, the campus security of the college the threat was directed at starts calling the girl. She never answers the calls and after a week contacts an administrator at the school asking that she be left alone as she wasn't sure why she was contacted.

The administrator then informs her of the above situation (that there was a threat on facebook). The administrator then tells her the reason campus security has been calling is because they are trying to help the girl keep from having to deal with the police directly. In the email he states that its out of the university's hands and that it is a police matter. He then asks her the two questions campus security was going to ask her:

1. Do the local police have anything to worry about?
2. Why had she posted the threat on her facebook profile?

Here are my questions:

1. In every case I can find, if the police find a death threat aimed at a school or individual they arrest within the week. If the police were going to arrest or charge her, wouldn't they have already done so for the reason of keeping anything from happening?

2. Would police really allow someone under investigation to be informed about the investigation? Wouldn't that allow a potential suspect to remove evidence or even flee?

3. If the police were to subpoena facebook, then the ISP that the hacker used to gain access and then post the threat with, eventually leading to the device the threat was posted from, how in the world could they prove who exactly sent the message from the device?

A lot of this whole story seems really fishy to me and if you need more details please let me know.