Yes, in your state, you may surreptitiously video- and even audiotape him, so long as you and he are the *only* participants in the conversation. If there is another person speaking with the former supervisor and you are not part of that conversation, then audiotaping them violates the law--your state treats it as illegal wiretapping--though you may continue videotaping. (The limitation on videotaping is that you must be in a public space, where is no or only a limited expectation of privacy.)