There is a case to be made for using the legal system as a deterrent. But there is also the case to made to not do that as in the case of Aaron Swartz.
This is a lot more localized and malicious. I do think people deserve second chances, but the context of all this rubs me the wrong way. Maybe the building owner was right to not make it a legal matter, but this feels like more than a harmless experiment. The malicious persons operational security is obviously terrible.
As someone who has done security research for over 15 years, I take the ethics of this sort of thing seriously. I fully expect repercussions of the legal sort if I did something like this without permission. The key detail being that this was done secretively in a private office.
Given the relative sophistication of it, it feels more like practice. In that case, not even a slap on the wrist very well could be seen as encouragement.