Is there a verb for making a statement/sentence milder or "dumbing it down"?
If the intent of the eyewitness is to make the event sound less horrifying to the listener, soft-pedal, minimize, or sugar-coat might work.
downplay
to treat or speak of (something) so as to reduce emphasis on its importance, value, strength, etc.: The press has downplayed the president's role in the negotiations.
Another verb is de-emphasize