The phrase "is a witness" is often used in legal contexts to refer to someone who observed an event or occurrence that is relevant to a case or investigation. There are several synonyms for this phrase that can be used to convey a similar meaning. These include "has seen," "observed," "noticed," "viewed," "witnessed," and "been present for." Depending on the context and tone of the text, some of these synonyms may be more appropriate than others. For example, "has seen" may be more formal and objective, while "observed" may be more subjective or personal. Overall, these synonyms can help to add variety and clarity to legal writing.