Well, thats a real wierd question, the answer being we rely on peoples statements And if they are opposed to each other (either ones own to ones own or others to ones own) then ???? Arise
In relation to the current renewed investigation into Madeleine McCann's disappearance ... why the concern over exactly where two men stood in the road nearly nine years ago?
The important thing is that both were in the street and concurred they were in conversation.
Jane Tanner was in the street and verified they were in conversation.
She also saw the other person who was present at the top of the street who could either have been the abductor or crèche man taking the long way home from the crèche.
You pays your money and you takes your choice on that one.
Of the three men Jane Tanner saw in that street that night we know who two were and what their business for being there was whichever side of the street they may have been standing on.
Can you think of any reason why the PJ did not track down crèche man at the time to carry out checks on him ... the sign in and sign out sheet would have sorted that out and once eliminated all resources could then have been concentrated on Smithman (all be it at a remove of thirteen days) and finding out who he might have been.