The king would have actually been made to look wiser if he had given time and opportunities to the suspects on purpose: if he had already had his own aide go through the documents earlier, without leaving a trace the suspects could recognise. Now he would have given the suspects a chance to prove their innocence by bringing in unaltered documents. Or prove their guilt by presenting documents the king's aide would immediately see aren't the same as he/she had checked earlier. Of course the unaltered documents were incriminating, so the suspects didn't have a choice, unless they were ready to confess. It's one thing to admit you made mistakes and face the consequences, but a totally different thing to try to hide earlier crimes by piling up more corruption on top of old corruption.
I guess this all shows the corruption in the kingdom reaches the king as well, unless the plot still has unrevealed twists.