Complex sentence: Connor knows there is a reason behind Branwell's silence, and he is sure that Branwell did not hurt Nikki, but Branwell is in a behavioral center, accused of a terrible crime and unable to speak for himself.
Split into simpler sentences: Connor knows there is a reason behind Branwell's silence, and he is sure that Branwell did not hurt Nikki. But Branwell is in a behavioral center, accused of a terrible crime and unable to speak for himself.