bystander

noun

1. A person who, although present at some event, does not take part in it; an observer, witness, or spectator.

   “If he wins, he will be at liberty, perhaps, to give vent to a laugh, or to pass a remark on the circumstance to a bystander, or to stake again, or to double his stake; but, even this he must do solely out of curiosity, and for the pleasure of watching the play of chances and of calculations, and not because of any vulgar desire to win.”

   “Conservative influencer Nick Sortor is handcuffed Thursday night by a police officer outside an ICE facility in Portland, Oregon, a bystander video shows; the video does not show events leading up to the arrest.”