Why do you think that Babushka Lady, the woman who was in Dealey Plaza when Kennedy was shot, did not come forward?  Or do you think that she did in fact come forward but that her story was covered up somehow?Here is a bit that Wikipedia has on her:

Babushka Lady was seen to be holding a camera by eyewitnesses and was also seen in film accounts of the assassination (such as this Muchmore frame and Zapruder Frame 285). She was observed standing on the grass between Elm and Main streets and she can be seen in the Zapruder film as well as in the films of Orville Nix,[1]  Marie Muchmore, and Mark Bell[2]  (44 seconds and 49 seconds into the Bell film: even though the shooting had already taken place and most of her surrounding witnesses took cover, she can be seen still standing with the camera at her face). After the shootings, she crossed Elm Street and joined the crowd that went up the grassy knoll in search of a gunman. She is last seen in photographs walking east on Elm Street and neither she nor the film she may have taken have been positively identified.[3]