I checked the DNS logs and found the exact date and time when the Pi was first seen in the network. I checked the RADIUS logs to see which employee was at the premises at that time and I saw multiple error messages that a deactivated account tried to connect to wifi.
That deactivated account belongs to an ex employee who (for some reason) made a deal with management that he could still have a key for a few months until he moved all his stuff out of the building (don't ask..).
中間的過程還蠻有趣的,包括研究是什麼擴充卡 (以及用途),然後從 SD card 上面挖資料,配合 Google 找線索,還有透過 WiGLE 定位,以及透過內部系統交叉比對,最後找到兇手...