I'm not a US citizen, so I don't know how vaguely phrased the wire tap laws are, but was this actually a wire tap?
As I understand it, the monitoring software allows remote access to the laptop, allowing files and screen grabs to be taken remotely. The phrase "wire tap" certainly brings to mind an interception of data which is already being transmitted.
Having said all that it's quite amusing. The teacher really should have noticed the low price and certainly the scratched off serial number. If she was a teacher at the school which owned the laptop, then she certainly should have been aware that the laptops were issued by the school and not owned by the students!
And whoever intercepted the "naughty" images really should have done a bit of editing. You only need the face of the "offender" to identify her, I doubt the police required her to drop her knickers and assume the position so they could make a positive ID!