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.
Are you claiming they were actually listening for someone else on the stairs..
How does one turn off one's hearing?
Not-to-mention that 'evidence of absence is not absence of evidence'
You've got it backwards.... as per usual