I'm guessing something was cut out out of this sentence and no one checked what was left, because I can't imagine someone writing it or an editor missing it. No author is cited. If you leave out "a witness said" it's fine. And attribution is helpful. "according to a witness" set off in commas would do the trick.
The rest of the sentence is:
". . . the Civic ran a red light while traveling eastbound on Dowling, striking a Jeep Wrangler ; the complaint said."A good example of why Strunk and White said to keep related words together.
Quote from the Alaska Dispatch News.