You now realize that Johan being a serial murderer is nothing more than a representation for all the people died as a result of hospital's loss of financial support when Tenma allowed the mayor to die.
That's why some of the earliest deaths are the Director (representing the director's life being destroyed by the scandal) and Tenma's own patient (representing his own accomplishments as a doctor being undone by his choice).
Tenma really was the killer all along, in a metaphorical sense.
I still don't get what was supposed to be good about that animu aside from m-muh ryona boner. It's Guilty Crown on steroids: absolute shit with good production values that would have been completely overlooked if not for its pretentiousness.
CG is easily the most overrated series on /a/.
I watched it 2 years ago, so it may not have aged well, but I found it pretty bad.
I'm not saying it's trash, but it's very far from the praise it gets.