Antonyms for the phrase "am a witness" are few and far in between. Some of the antonyms that come to mind include "am not a witness," "am unaware," and "am ignorant." However, these antonyms might not always be appropriate, as being a witness is often considered a duty and responsibility. It is essential to bear in mind that being a witness is not only limited to legal proceedings but also applies to everyday life. To be a witness means to observe and testify to the truth, which is an essential aspect of accountability and transparency. Therefore, in most situations, there are no antonyms for being a witness.