Consider a court case. A jury hears the witnesses placed on the stand. Each witness would be individually interviewed, giving an account of the same event which would be written (most likely by an officer) apart from other witnesses, very likely at different times, so that there's no collusion between witnesses. The eyewitness accounts help the Jury understand an event and is a part of their decision making.
They brought horses. It was easier for them to catch up with the buffalo and hunt instead of having to throw weapons from a far and run after the Buffalo.
