be witness to something
be (a) witness to (something)
1. To see something happen. I was a witness to many inappropriate situations when I worked in an office. Were you witness to the accident, or did you arrive at the scene after it happened?
2. To be proof of something. The many students on campus these days are a witness to the school's successful rebranding efforts.
See also: witness
be (a) ˈwitness to something
1 (formal) see something take place: He has been witness to a terrible murder.
2 (written) show that something is true; provide evidence for something: His good health is a witness to the success of the treatment.