He did try and assassinate General Edwin Walker a few month earlier. Seems like if you can shoot at one politician you can shoot at a second one https://www.history.com/news/lee-harvey-oswald-other-target
Bill Paxton was in Fort Worth at his speech just a few hours before the assassination. On his dads shoulders in the picture
One of the more convincing things I've seen wrt to it being a single shooter. Only 4 mins but if you're elite ADHD you can just watch the last minute...