I understand the frustration of the ending. I was going to write off this movie as bad. Then I thought for a little bit.
Here's my theory: I believe Albert wasn't the killer. I know that's a common consensus. I don't think Deke or Jimmy was either. However, the confusion and frustration of not getting an answer from the film is actually the result expected. We, as an audience, are to feel just as lost and frustrated with the unknown and unresolved as Deke and Jimmy do. To feel just like how it is to be a obsessive Detective to the point where your perception has become so skewed from obsession, you're desperate for an answer. To the point where you break and it has consequences. Perhaps to show us how being a dedicated detective has its weight that finally breaks them down. Deke knows this finally, as Jimmy's situation wakes him up, however, he doesn't want Jimmy to become him. Thus buying the red clip to assure Jimmy that Albert was actually the killer, thus making him feel justified in killing him. While in reality, it wasn't Albert and it's another burden that Deke has to carry on with within his conscious.
All in all, I believe the movie is to show the best of the best get a breaking point at some point, not wanting to admit defeat or that they just aren't as good as they used to be. Because all the sacrifices they give to dedicate their time into finding the killer or victims, they want it to be time that was well spent instead of time wasted making their life miserable.
Here's my theory: I believe Albert wasn't the killer. I know that's a common consensus. I don't think Deke or Jimmy was either. However, the confusion and frustration of not getting an answer from the film is actually the result expected. We, as an audience, are to feel just as lost and frustrated with the unknown and unresolved as Deke and Jimmy do. To feel just like how it is to be a obsessive Detective to the point where your perception has become so skewed from obsession, you're desperate for an answer. To the point where you break and it has consequences. Perhaps to show us how being a dedicated detective has its weight that finally breaks them down. Deke knows this finally, as Jimmy's situation wakes him up, however, he doesn't want Jimmy to become him. Thus buying the red clip to assure Jimmy that Albert was actually the killer, thus making him feel justified in killing him. While in reality, it wasn't Albert and it's another burden that Deke has to carry on with within his conscious.
All in all, I believe the movie is to show the best of the best get a breaking point at some point, not wanting to admit defeat or that they just aren't as good as they used to be. Because all the sacrifices they give to dedicate their time into finding the killer or victims, they want it to be time that was well spent instead of time wasted making their life miserable.