I think it would be a mistake to draw any inference from the fact that Brueckner has not, so far, been charged with anything connected to Madeleine's disappearance:
Convicted rapist Brueckner, 45, was named as the man responsible for Madeleine's May 2007 abduction two years ago by German police in a fanfare which sparked worldwide media attention
www.dailymail.co.uk
Consider these two paragraphs from the article I link to above:
Instead, German investigators today charged [Brueckner] with five offences between 2000 and 2017, when Brueckner was travelling between his native Germany and Portugal.
These include the rapes of two unknown women in Portugal, the rape of a 20-year-old Irish woman in 2004, the sexual abuse of a 10-year-old German girl in April 2007 on a Portuguese beach - close to where Madeleine vanished just a month later - and a further sexual abuse case in 2017, again in Portugal.
These are all crimes committed, as long ago as 2000. which Brueckner has been charged with, but has yet to be tried for.
Consider, further, that Brueckner only came onto the German radar in respect of alleged crimes against Madeleine well after 2007.
Small wonder, then, that no charges have, so far, been pressed against Brueckner
in respect of crimes against Madeleine.
There is a long queue, and Madeleine has her place in that queue.
ETA: One line of sceptic-reasoning for accusing the McCanns blown out of the water is that crimes of the type Madeleine was a victim of are committed by serial offenders and the crime against Madeleine was 'one-off and unique'. Oh no it wasn't.
Hazel Behan's case has, I think, still to come to trial.
She was raped in 2004, three years before Madeleine vanished
Hazel Behan, now 39, was raped at knifepoint inside a holiday apartment in Praia da Rocha, Portugal, in June 2004 by a man she believes is Christian Brueckner.
www.dailymail.co.uk