Even if the scope were misaligned, a shooter who practiced with that rifle could compensate for any deficiency.
Huh? Use some logic for a change. They needed to plant a bullet that could positively be matched to the planted rifle. Comprende?
I hear it has been done, but have never seen a specific reference or video. Ot to put it another way we can put to bed to tale that people have duplicated the feat on video
Even Gary Mack admitted that he himself, a middle aged old man at the time, could run down the stairs as quick as Oswald.
Perhaps you should read "Girl on the Stairs"... Vicky Adams and Sandy Styles were on the stairs and they saw or heard NOBODY.