When they arrived back from Portugal there was a denial;
"Despite there being so much we wish to say we are unable to do so, except to say this: we played no part in the disappearance of our lovely daughter, Madeleine."
https://www.dailymail.co.uk/news/article-480801/Madeleines-parents-fly-home-say-We-played-disappearance.html
From that article and a reminder of what was being reported in all the papers here and in Portugal at the time:
The main plank of the police case so far is that they believe Mrs McCann, 39, accidentally gave Madeleine a fatal overdose of sedative and then conspired with her husband in an incredible cover-up.
There are growing fears, however, that they are pursuing a cynical strategy of using the forensic evidence, scant as it may be, to force - or possibly even trick - the couple into confessing.
They are said to be steadily increasing the pressure on the McCanns, including making leaks to the Portuguese media.
It was reported yesterday in one Portuguese newspaper that detectives are working on the theory that Mrs McCann may have been taking a sedative herself because she is "mentally unbalanced" - and somehow gave a dose to her three-year-old daughter by mistake.
Another said Mr McCann admitted during his interview that he, not his wife, administered the lethal dose.