I voted DWAP. I just couldn't pull the trigger on my interpretation of the "the darkness he desperately seeks to expose." I understood Blake to mean the darkness was a perception of a dark side to a family, organization, culture or society.
I see your point. Like I said, I just couldn't quite get past the last segment of the logline. The Jimmy Stewart character does go down the dark ally as he becomes a voyeur, a requirement of the WHYDUNIT. He even seems addicted to it, to detriment of his relationship with his girlfriend.
I chose DWAP because in this story, he is a common individual. His photographic skills are nullified because he can't go out and take pictures. Through his observations of the neighbors, he becomes involved in a possible murder. I agree he begins to investigate which leads to his encounter with the antagonist.
However, that encounter was the result, not of his investigation, but of his voyeurism.
"The standard doesn't change."-Mike Tomlin