The salient points would be: 1) was I carrying a child through the streets that night, 2)did I pass the spot where the Smiths say they saw me, 3) do I remember passing a big group of tourists. If the answer was yes to two or more of those and I was not an abductor then I can think of no reason why I should fear coming forward to be eliminated, and minor errors in the reconstruction would not deter me from doing so. However, I'm wondering if Smithman might have been a tourist from a country where maybe there was not so much coverage of the case after the initial few days, maybe Russia perhaps? He may still to this day have no inkling that he is a "wanted" man. Do you get many Russians holidaying in PdL?
At last, a fairly intelligent post on how to crack this particular nut. Do it the 'wrong' way round. Stop worrying about what the Smiths saw, which has produced nothing, and start role playing Smithman.

I have never yet met a Russian holidaying in Luz, though I have met more than one Russian person working here (and presumably living here).
So, let me be Smithman in this version, (and let me be Portuguese,) and let me be innocent. The last bit is obvious. I am not coming forward if I am guilty, after all.
What do I get for coming forward? A very, very large pile of poo. Given that I am innocent, do I wish to endure such torment? Why? Do you think for a moment that whatever-his-name is, the guy with a partner and a young child, but labelled the pig-farmer-rapist, enjoyed being hauled to Faro in Dec 14, and exposed to the media, at the behest of OG?
Roughly speaking, there is the right to forget here i.e. go straight and after a certain length of time previous crimes are supposed to be forgotten. The pig farmer committed a crime which has absolutely NOTHING in common with the Madeleine case, other than it occurred in Luz.
So if that is what he got first time round (PJ/media), and that is what he got second time round (OG/media), are you actually telling me you would hand yourself on a plate to gutter media?
Honestly?
You would decide it was your civic duty to be grilled by the Portuguese police, grilled by OG, then grilled by the media?
Would you really put your family through that?
I'm not Smithman, but let me answer my own question. As it happens, I have no criminal record. However, I would not subject myself to such an ordeal, given that this trial by fire does not solve the case. I certainly would not expose my family to the poking and prying of the media.
To suggest Smithman has nothing to fear by coming forward is naïve. The Smiths supposedly had nothing to fear; they came forward; and it would appear that at least Mr Smith considered they suffered greatly. If they had known in advance what they would go through, would the Smiths have come forward anyway? Only they can answer that.