The parents could also be charged

Of negligence if they were wrong in this regard. If the father was there all the times but left for just a few minutes, then Zhang thought he had a chance to sexually assault the little girl without leaving DNA traces, that could happen.

Any way, when police make an arrest on such calls, they don't simply arrest without collecting necessary evidence. When AD's offices make a case, they evaluate all evidence and prepare for necessary materials for their case.

It is true that in China, sometimes, a victim's yelling is considered for adult rape cases, but never for underaged. 

Nobody can assume this verdict was made not wrong, but there is a civil case remaining unconcluded, and the prisoner can always appeal. Just don't blame victim's parents for any mistakes you can also make when you are not sitting in front of your computer.