eyewitness

Etymology

eye + witness

noun

1. Someone who sees an event and can report or testify about it. [from 16th c.]
   And the girl's fate he could picture as plainly as though he were an eyewitness to it. 1915, Edgar Rice Burroughs, The Return of Tarzan
   The evidence of eyewitnesses and the distance travelled after the initial derailment confirmed that the train was travelling at 45 to 50 m.p.h. as it became derailed. 1960 September, “Talking of Trains: Accident at Holmes Chapel”, in Trains Illustrated, page 522

verb

1. To be present at an event, and see it