Almost as a guide line, they could use the WIFI laws to define if he had illegal intent.

If my home network is set up on an open WAP with no filtering or WEP/WPA and the SID open and available, anyone who is in range of my WAP is then allowed to connect to it and gain free internet access. (not access to my network computers though) In fact, it would be hard for them to not connect to it, if there is not another WAP also in range that they could connect to also.

As soon as I disable the SID broadcast, and or make use of WEP/WPA and IP/MAC filtering then for them to bypass these protections and connect to my WAP (for any reason) is illegal.

This guy though, even if he didn't use any 'hacking/cracking' tools, went into the system and copied data from it. If it was a wired system, he would have to have made a physical connection, like openning a closed door. Even on a wireless system, to gain entry to the network computors he would have had to purposefully made a connection through the netbios or some other means.

Just being curious can not be used as an excuse. That would be like being a guest in somebodies home, and poking through their drawers and cabnits. And then taking what ever he wanted.

At the very least it would be an invasion of privacy, and then to take things would be componded into theft.