You prove to them that you're not guilty by agreeing to answer all questions honestly and offer to do a reconstruction to cover and explain any discrepancies that they have in the timeline. If you do all to help then chances are they will believe you are telling the truth. Actions speak louder than words.
Until the day they were made Arguidos they had co-operated fully and answered all questions honestly - and look where that got them. IMO the PJ were not interested in 'answers' they just wanted confessions because they had no evidence against the McCanns - and time was running out as the laws were about to change.
The McCanns had not been asked to do a reconstructon - that was the PJ's decision. However as already discussed, the only thing a reconstruction would have proved is that it is impossible for 10 people to accurately recreate - down to the minute - their various movements on 3rd May unless they could recall the exact times they had made them. Unsurprisingly - 9 out of 10 of them couldn't do that.
Discrepancies would be expected by normal police officers when so many people were involved. If there were huge unexplained discrepancies amongst the various statements - then why didn't the PJ make the whole group Arguidos?
The fact that the PJ 'ploy' to lie about 100% DNA match failed so miserably - should have told them something - as the McCanns (particularly as they were doctors) would
know that if they were guilty - and there was a 100% DNA match to prove that - then it would be 'game over' - and it would be pointless to carry on. IMO they would have confessed at that point.
The fact that the DNA 'Ace' didn't have that desired affect should have told the PJ that in suspecting the McCanns they were barking up the wrong tree - as SY and the Oporto team have since confirmed.
No normal sane person would want to stay in a foreign country where the blatently obvious aim of the police force was to arrest them for a crime which they knew they had not committed.
AIMHO