Saw this on CNN:

Young teen girl gets a MySpace account, receives nice messages from a boy but they quickly turn into violent messages, girl gets so depressed that she hangs herself.

It turns out the "boy" was actually a mother down the street who wanted to know why the teen was in an argument with her own daughter.

Prosecutors, sheriff, and FBI aren't investigating. A year has gone by since the incident.

What makes this legal? If the violent messages were received in the mail or in a note, would the outcome still be the same?