eye ‧ wit ‧ ness /ˈaɪˌwɪtnəs, ˈaɪˌwɪtnɪs/ BrE AmE noun [countable]
someone who has seen something such as a crime happen, and is able to describe it afterwards
eyewitness account/report/testimony
According to eyewitness accounts, soldiers opened fire on the crowd.
One eyewitness said he saw her talking to a man in a blue car.