So that's a bunch of bodies in the water at the end? The biggest hole is obviously how did Linden suddenly find the buildings/trees/pond after 4 years? She wasn't motivated to find it earlier? Is the setup supposed to be that the Dad is the killer and he took the kid with him to the pond a bunch? I presume that isn't how it will play out.
........ I never felt like the detectives behaved in a rational manner.
Yes, the number of bodies signifies that since Linden and the Lt first closed the case, that the original killer has been still killing all of this time. Because he kills "street" children who have slipped through the cracks of the system, to mostly parents who are gone, on drugs or don't care, no one notices and no one reports them missing. If they are reported missing, no vast amount of resources are put into it.
Linden believes these killings all tie in to the original case, that was closed, and the result was Saarsgard on death row. The Lt believes or acts as if the killings now are separate, that Linden can't detach from the case personally and doesn't want to create a situation where Saarsgard can get out of execution by something Linden does or finds or theorizes.
When Linden first dealt with the child, who was locked in a room with his murdered mother, the child only drew the trees and the tree line. At the time, the picture meant nothing or could be construed several ways. One argument, I think that was discussed last season when Linden was in the psych ward was that it was coping response by the boy. When Linden visits the boy again in the S3 pilot, it's the same treeline picture, but now with houses to the side and I think a dock. Then Linden goes to try to recreate where the boy would have needed to be, to have locked in that image and want to draw it over and over again. By doing this, she searches the area and finds the bodies. It was the increased detail in the 2nd photo she found recently on the wall of the childs room that led her there.
It's implied that the case, when she was on it originally, caused her massive emotional trauma and now it's revealed she was banging the married Lieutenant at the time. In S1 or S2, she uses a resource who was a former partner that Holder figures out that she slept with. So that's two former partners that Linden has slept with. She states she had doubts about the father (Saarsgard) as the killer, but there was too much on her plate to argue it. She was also outranked and the city and the department wanted a high profile case closed.
The inference is that whether or not the father is the killer, his son was exposed enough to that area, to have memorized, even at a young age, the treeline and drew it over and over again. This implies while the father might not be the killer, it's evident he knows something he's not saying upfront right now.
His behavioral model, attacking the priest, getting close to attacking the guard, making threats, being difficult, demanding to be hanged, seems to be his way of ensuring he will die and that the death will form some type of satisfaction. His? Doubtful. Someone else? Probably. Why would a man do that? A man would do that if he thought a failure to comply and take the fall would mean his family would be killed for it. That's the only leverage the show has given, his surviving child. Clearly someone on the outside wants him dead, wants his case closed and wants the public to have no doubts that he was the killer.
The problem with procedural aspect of the show is that a genuine "redball", a high profile public case, would be serviced by an entire unit, not just a couple of detectives. The show seems to soften this some by introducing a new partner for Holder and a former partner for Linden, except both seem conveniently placed to be disposable to get any potential S4 with Linden and Holder back together out of necessity. Holder current partner is a roadblock. By the end of the season, he will be transferred, guilty, disgraced, retired or dead. This is like the Lion King and realizing Mufasa has to die for Simba to get to the point of learning to grow up. Obi Wan dies so Luke has to grow up. Sonny Corleone dies so Michael can take over the family.
Where Veena Sud is failing is the lack of other detectives and the lack of other concurrent cases. While their is a primary arc, the show does little in the way of secondary arcs and character development. This is why there are so many red herrings, to time fill.
A better example of what The Killing could be would be the BBC's Wire In The Blood. Watching Wire in the Blood shows how "gimmicky" The Killing can be at times.