In the absence of a statement by Mr Smith that is pure speculation on your part. Mr Smith has never declared publicly that he changed his mind.
I have to agree with 'ferryman' here and respectfully suggest that it is far from 'speculation' that Martin Smith 'changed his mind'.
Surely it is obvious that he did for these among the following reasons:
1. He was publicly quoted in the media in 2008 as supporting the abduction, asking people to help in the search for Madeleine and look for the abductor (forget the exact quote)
2. He agreed as early as December 2007 or January 2008 to speak to Brian Kennedy and Metodo 3, knowing that they were acting for the McCanns
3. He clearly subsequently agreed to at least put his name to the two e-fits (whatever doubts I and not a few others have about his capacity to do so, a year after the event
4. Almost certainly he consented to the McCanns suggesting twice, within the May 2009 Channel 4 'Mockumentary, strongly suggesting that Smithman and Tannerman were one and the same
5. Again he must be presumed to have consented to an audio summary of his evidence being placed on the McCanns' website in May 2009 (and it's still there today, 7 years later)
6. His evidence was used by Kate McCann again in 7 pages of her book, 'madeleine' (May 2011) to advance the case that Smithman and Tannerman were one and the same, and finally
7. His two admitted meetings with DCI Andy Redwood, one in 2012 and the other in 2013, must again be taken as presumed, if not proactive, co-operation with BBC Crimewatch, who in their show of 14 October 2013 made the two efits, quote, 'the centre of our focus'.
The only way in which you can argue
@ John that he did not willingly 'change his mind' would be to suggest that he has been threatened, or otherwise forced, to change his mind.
(I leave out from this post all the many obvious issues that arise from his controversial evidence, given 4.5 months after the event, that he was '60% to 80% sure' it was Gerry McCann that he had seen 4.5 months earlier, based basically on his claim that Gerry was carrying Sean over his shoulder the same way as the man he alleged that he'd seen)