Given that the Modus Operandi of office psychopaths is fairly well doented, is it easy to look for a ....?

To expand a bit on li's answer, also watch the behavior of the remaining staff. People tend give a nice long "exhale" once a person like that leaves. Watch everyone to see if they are more relaxed, listen to what they say, for example one staff member might remark "I can finally place the stapler here again" or "We can have our colorful coffee cups on our desk again without an issue" If they remark on little changes they are allowed to make, it is perhaps b/c they are no longer being terrorized by said co-worker.